From 55d6af1d66885059ffc2ac23083de52d12be63bb Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:54 +0206 Subject: [PATCH 1/7] lib/nmi_backtrace: explicitly serialize banner and regs Currently the nmi_backtrace is serialized against other CPUs because the messages are sent to the NMI buffers. Once these buffers are removed, only the dumped stack will be serialized against other CPUs (via the printk_cpu_lock). Also serialize the nmi_backtrace banner and regs using the printk_cpu_lock so that per-CPU serialization will be preserved even after the NMI buffers are removed. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-2-john.ogness@linutronix.de --- lib/nmi_backtrace.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c index 8abe1870dba4..dae233c5f597 100644 --- a/lib/nmi_backtrace.c +++ b/lib/nmi_backtrace.c @@ -92,17 +92,24 @@ module_param(backtrace_idle, bool, 0644); bool nmi_cpu_backtrace(struct pt_regs *regs) { int cpu = smp_processor_id(); + unsigned long flags; if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) { if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) { pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n", cpu, (void *)instruction_pointer(regs)); } else { + /* + * Allow nested NMI backtraces while serializing + * against other CPUs. + */ + printk_cpu_lock_irqsave(flags); pr_warn("NMI backtrace for cpu %d\n", cpu); if (regs) show_regs(regs); else dump_stack(); + printk_cpu_unlock_irqrestore(flags); } cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); return true; From 002eb6ad075142e5940122c7fcee71cf1e906e29 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:55 +0206 Subject: [PATCH 2/7] printk: track/limit recursion Currently the printk safe buffers provide a form of recursion protection by redirecting to the safe buffers whenever printk() is recursively called. In preparation for removal of the safe buffers, provide an alternate explicit recursion protection. Recursion is limited to 3 levels per-CPU and per-context. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-3-john.ogness@linutronix.de --- kernel/printk/printk.c | 86 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 83 insertions(+), 3 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 142a58d124d9..7fa0b4d91975 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1940,6 +1940,76 @@ static void call_console_drivers(const char *ext_text, size_t ext_len, } } +/* + * Recursion is tracked separately on each CPU. If NMIs are supported, an + * additional NMI context per CPU is also separately tracked. Until per-CPU + * is available, a separate "early tracking" is performed. + */ +static DEFINE_PER_CPU(u8, printk_count); +static u8 printk_count_early; +#ifdef CONFIG_HAVE_NMI +static DEFINE_PER_CPU(u8, printk_count_nmi); +static u8 printk_count_nmi_early; +#endif + +/* + * Recursion is limited to keep the output sane. printk() should not require + * more than 1 level of recursion (allowing, for example, printk() to trigger + * a WARN), but a higher value is used in case some printk-internal errors + * exist, such as the ringbuffer validation checks failing. + */ +#define PRINTK_MAX_RECURSION 3 + +/* + * Return a pointer to the dedicated counter for the CPU+context of the + * caller. + */ +static u8 *__printk_recursion_counter(void) +{ +#ifdef CONFIG_HAVE_NMI + if (in_nmi()) { + if (printk_percpu_data_ready()) + return this_cpu_ptr(&printk_count_nmi); + return &printk_count_nmi_early; + } +#endif + if (printk_percpu_data_ready()) + return this_cpu_ptr(&printk_count); + return &printk_count_early; +} + +/* + * Enter recursion tracking. Interrupts are disabled to simplify tracking. + * The caller must check the boolean return value to see if the recursion is + * allowed. On failure, interrupts are not disabled. + * + * @recursion_ptr must be a variable of type (u8 *) and is the same variable + * that is passed to printk_exit_irqrestore(). + */ +#define printk_enter_irqsave(recursion_ptr, flags) \ +({ \ + bool success = true; \ + \ + typecheck(u8 *, recursion_ptr); \ + local_irq_save(flags); \ + (recursion_ptr) = __printk_recursion_counter(); \ + if (*(recursion_ptr) > PRINTK_MAX_RECURSION) { \ + local_irq_restore(flags); \ + success = false; \ + } else { \ + (*(recursion_ptr))++; \ + } \ + success; \ +}) + +/* Exit recursion tracking, restoring interrupts. */ +#define printk_exit_irqrestore(recursion_ptr, flags) \ + do { \ + typecheck(u8 *, recursion_ptr); \ + (*(recursion_ptr))--; \ + local_irq_restore(flags); \ + } while (0) + int printk_delay_msec __read_mostly; static inline void printk_delay(void) @@ -2040,11 +2110,14 @@ int vprintk_store(int facility, int level, struct prb_reserved_entry e; enum log_flags lflags = 0; struct printk_record r; + unsigned long irqflags; u16 trunc_msg_len = 0; char prefix_buf[8]; + u8 *recursion_ptr; u16 reserve_size; va_list args2; u16 text_len; + int ret = 0; u64 ts_nsec; /* @@ -2055,6 +2128,9 @@ int vprintk_store(int facility, int level, */ ts_nsec = local_clock(); + if (!printk_enter_irqsave(recursion_ptr, irqflags)) + return 0; + /* * The sprintf needs to come first since the syslog prefix might be * passed in as a parameter. An extra byte must be reserved so that @@ -2092,7 +2168,8 @@ int vprintk_store(int facility, int level, prb_commit(&e); } - return text_len; + ret = text_len; + goto out; } } @@ -2108,7 +2185,7 @@ int vprintk_store(int facility, int level, prb_rec_init_wr(&r, reserve_size + trunc_msg_len); if (!prb_reserve(&e, prb, &r)) - return 0; + goto out; } /* fill message */ @@ -2130,7 +2207,10 @@ int vprintk_store(int facility, int level, else prb_final_commit(&e); - return (text_len + trunc_msg_len); + ret = text_len + trunc_msg_len; +out: + printk_exit_irqrestore(recursion_ptr, irqflags); + return ret; } asmlinkage int vprintk_emit(int facility, int level, From 93d102f094be9beab28e5afb656c188b16a3793b Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:56 +0206 Subject: [PATCH 3/7] printk: remove safe buffers With @logbuf_lock removed, the high level printk functions for storing messages are lockless. Messages can be stored from any context, so there is no need for the NMI and safe buffers anymore. Remove the NMI and safe buffers. Although the safe buffers are removed, the NMI and safe context tracking is still in place. In these contexts, store the message immediately but still use irq_work to defer the console printing. Since printk recursion tracking is in place, safe context tracking for most of printk is not needed. Remove it. Only safe context tracking relating to the console and console_owner locks is left in place. This is because the console and console_owner locks are needed for the actual printing. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-4-john.ogness@linutronix.de --- arch/powerpc/kernel/traps.c | 1 - arch/powerpc/kernel/watchdog.c | 5 - include/linux/printk.h | 10 - kernel/kexec_core.c | 1 - kernel/panic.c | 3 - kernel/printk/internal.h | 17 -- kernel/printk/printk.c | 120 +++++------- kernel/printk/printk_safe.c | 335 +-------------------------------- lib/nmi_backtrace.c | 6 - 9 files changed, 48 insertions(+), 450 deletions(-) diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index b4ab95c9e94a..2522800217d1 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -170,7 +170,6 @@ extern void panic_flush_kmsg_start(void) extern void panic_flush_kmsg_end(void) { - printk_safe_flush_on_panic(); kmsg_dump(KMSG_DUMP_PANIC); bust_spinlocks(0); debug_locks_off(); diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c index c9a8f4781a10..dc17d8903d4f 100644 --- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -183,11 +183,6 @@ static void watchdog_smp_panic(int cpu, u64 tb) wd_smp_unlock(&flags); - printk_safe_flush(); - /* - * printk_safe_flush() seems to require another print - * before anything actually goes out to console. - */ if (sysctl_hardlockup_all_cpu_backtrace) trigger_allbutself_cpu_backtrace(); diff --git a/include/linux/printk.h b/include/linux/printk.h index d796183f26c9..719d919f9b67 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -208,8 +208,6 @@ void dump_stack_print_info(const char *log_lvl); void show_regs_print_info(const char *log_lvl); extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold; extern asmlinkage void dump_stack(void) __cold; -extern void printk_safe_flush(void); -extern void printk_safe_flush_on_panic(void); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -277,14 +275,6 @@ static inline void dump_stack_lvl(const char *log_lvl) static inline void dump_stack(void) { } - -static inline void printk_safe_flush(void) -{ -} - -static inline void printk_safe_flush_on_panic(void) -{ -} #endif #ifdef CONFIG_SMP diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index f099baee3578..69c6e9b7761c 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -978,7 +978,6 @@ void crash_kexec(struct pt_regs *regs) old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu); if (old_cpu == PANIC_CPU_INVALID) { /* This is the 1st CPU which comes here, so go ahead. */ - printk_safe_flush_on_panic(); __crash_kexec(regs); /* diff --git a/kernel/panic.c b/kernel/panic.c index 332736a72a58..1f0df42f8d0c 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -247,7 +247,6 @@ void panic(const char *fmt, ...) * Bypass the panic_cpu check and call __crash_kexec directly. */ if (!_crash_kexec_post_notifiers) { - printk_safe_flush_on_panic(); __crash_kexec(NULL); /* @@ -271,8 +270,6 @@ void panic(const char *fmt, ...) */ atomic_notifier_call_chain(&panic_notifier_list, 0, buf); - /* Call flush even twice. It tries harder with a single online CPU */ - printk_safe_flush_on_panic(); kmsg_dump(KMSG_DUMP_PANIC); /* diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 51615c909b2f..6cc35c5de890 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -22,7 +22,6 @@ __printf(1, 0) int vprintk_deferred(const char *fmt, va_list args); void __printk_safe_enter(void); void __printk_safe_exit(void); -void printk_safe_init(void); bool printk_percpu_data_ready(void); #define printk_safe_enter_irqsave(flags) \ @@ -37,18 +36,6 @@ bool printk_percpu_data_ready(void); local_irq_restore(flags); \ } while (0) -#define printk_safe_enter_irq() \ - do { \ - local_irq_disable(); \ - __printk_safe_enter(); \ - } while (0) - -#define printk_safe_exit_irq() \ - do { \ - __printk_safe_exit(); \ - local_irq_enable(); \ - } while (0) - void defer_console_output(void); #else @@ -61,9 +48,5 @@ void defer_console_output(void); #define printk_safe_enter_irqsave(flags) local_irq_save(flags) #define printk_safe_exit_irqrestore(flags) local_irq_restore(flags) -#define printk_safe_enter_irq() local_irq_disable() -#define printk_safe_exit_irq() local_irq_enable() - -static inline void printk_safe_init(void) { } static inline bool printk_percpu_data_ready(void) { return false; } #endif /* CONFIG_PRINTK */ diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 7fa0b4d91975..219ad710a9e8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -732,27 +732,22 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, if (ret) return ret; - printk_safe_enter_irq(); if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) { if (file->f_flags & O_NONBLOCK) { ret = -EAGAIN; - printk_safe_exit_irq(); goto out; } - printk_safe_exit_irq(); ret = wait_event_interruptible(log_wait, prb_read_valid(prb, atomic64_read(&user->seq), r)); if (ret) goto out; - printk_safe_enter_irq(); } if (r->info->seq != atomic64_read(&user->seq)) { /* our last seen message is gone, return error and reset */ atomic64_set(&user->seq, r->info->seq); ret = -EPIPE; - printk_safe_exit_irq(); goto out; } @@ -762,7 +757,6 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, &r->info->dev_info); atomic64_set(&user->seq, r->info->seq + 1); - printk_safe_exit_irq(); if (len > count) { ret = -EINVAL; @@ -797,7 +791,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) if (offset) return -ESPIPE; - printk_safe_enter_irq(); switch (whence) { case SEEK_SET: /* the first record */ @@ -818,7 +811,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) default: ret = -EINVAL; } - printk_safe_exit_irq(); return ret; } @@ -833,7 +825,6 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait) poll_wait(file, &log_wait, wait); - printk_safe_enter_irq(); if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) { /* return error when data has vanished underneath us */ if (info.seq != atomic64_read(&user->seq)) @@ -841,7 +832,6 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait) else ret = EPOLLIN|EPOLLRDNORM; } - printk_safe_exit_irq(); return ret; } @@ -874,9 +864,7 @@ static int devkmsg_open(struct inode *inode, struct file *file) prb_rec_init_rd(&user->record, &user->info, &user->text_buf[0], sizeof(user->text_buf)); - printk_safe_enter_irq(); atomic64_set(&user->seq, prb_first_valid_seq(prb)); - printk_safe_exit_irq(); file->private_data = user; return 0; @@ -1042,9 +1030,6 @@ static inline void log_buf_add_cpu(void) {} static void __init set_percpu_data_ready(void) { - printk_safe_init(); - /* Make sure we set this flag only after printk_safe() init is done */ - barrier(); __printk_percpu_data_ready = true; } @@ -1082,6 +1067,7 @@ void __init setup_log_buf(int early) struct prb_desc *new_descs; struct printk_info info; struct printk_record r; + unsigned int text_size; size_t new_descs_size; size_t new_infos_size; unsigned long flags; @@ -1142,24 +1128,37 @@ void __init setup_log_buf(int early) new_descs, ilog2(new_descs_count), new_infos); - printk_safe_enter_irqsave(flags); + local_irq_save(flags); log_buf_len = new_log_buf_len; log_buf = new_log_buf; new_log_buf_len = 0; free = __LOG_BUF_LEN; - prb_for_each_record(0, &printk_rb_static, seq, &r) - free -= add_to_rb(&printk_rb_dynamic, &r); + prb_for_each_record(0, &printk_rb_static, seq, &r) { + text_size = add_to_rb(&printk_rb_dynamic, &r); + if (text_size > free) + free = 0; + else + free -= text_size; + } - /* - * This is early enough that everything is still running on the - * boot CPU and interrupts are disabled. So no new messages will - * appear during the transition to the dynamic buffer. - */ prb = &printk_rb_dynamic; - printk_safe_exit_irqrestore(flags); + local_irq_restore(flags); + + /* + * Copy any remaining messages that might have appeared from + * NMI context after copying but before switching to the + * dynamic buffer. + */ + prb_for_each_record(seq, &printk_rb_static, seq, &r) { + text_size = add_to_rb(&printk_rb_dynamic, &r); + if (text_size > free) + free = 0; + else + free -= text_size; + } if (seq != prb_next_seq(&printk_rb_static)) { pr_err("dropped %llu messages\n", @@ -1498,11 +1497,9 @@ static int syslog_print(char __user *buf, int size) size_t n; size_t skip; - printk_safe_enter_irq(); - raw_spin_lock(&syslog_lock); + raw_spin_lock_irq(&syslog_lock); if (!prb_read_valid(prb, syslog_seq, &r)) { - raw_spin_unlock(&syslog_lock); - printk_safe_exit_irq(); + raw_spin_unlock_irq(&syslog_lock); break; } if (r.info->seq != syslog_seq) { @@ -1531,8 +1528,7 @@ static int syslog_print(char __user *buf, int size) syslog_partial += n; } else n = 0; - raw_spin_unlock(&syslog_lock); - printk_safe_exit_irq(); + raw_spin_unlock_irq(&syslog_lock); if (!n) break; @@ -1566,7 +1562,6 @@ static int syslog_print_all(char __user *buf, int size, bool clear) return -ENOMEM; time = printk_time; - printk_safe_enter_irq(); /* * Find first record that fits, including all following records, * into the user-provided buffer for this dump. @@ -1587,23 +1582,20 @@ static int syslog_print_all(char __user *buf, int size, bool clear) break; } - printk_safe_exit_irq(); if (copy_to_user(buf + len, text, textlen)) len = -EFAULT; else len += textlen; - printk_safe_enter_irq(); if (len < 0) break; } if (clear) { - raw_spin_lock(&syslog_lock); + raw_spin_lock_irq(&syslog_lock); latched_seq_write(&clear_seq, seq); - raw_spin_unlock(&syslog_lock); + raw_spin_unlock_irq(&syslog_lock); } - printk_safe_exit_irq(); kfree(text); return len; @@ -1611,11 +1603,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear) static void syslog_clear(void) { - printk_safe_enter_irq(); - raw_spin_lock(&syslog_lock); + raw_spin_lock_irq(&syslog_lock); latched_seq_write(&clear_seq, prb_next_seq(prb)); - raw_spin_unlock(&syslog_lock); - printk_safe_exit_irq(); + raw_spin_unlock_irq(&syslog_lock); } /* Return a consistent copy of @syslog_seq. */ @@ -1703,12 +1693,10 @@ int do_syslog(int type, char __user *buf, int len, int source) break; /* Number of chars in the log buffer */ case SYSLOG_ACTION_SIZE_UNREAD: - printk_safe_enter_irq(); - raw_spin_lock(&syslog_lock); + raw_spin_lock_irq(&syslog_lock); if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) { /* No unread messages. */ - raw_spin_unlock(&syslog_lock); - printk_safe_exit_irq(); + raw_spin_unlock_irq(&syslog_lock); return 0; } if (info.seq != syslog_seq) { @@ -1736,8 +1724,7 @@ int do_syslog(int type, char __user *buf, int len, int source) } error -= syslog_partial; } - raw_spin_unlock(&syslog_lock); - printk_safe_exit_irq(); + raw_spin_unlock_irq(&syslog_lock); break; /* Size of the log buffer */ case SYSLOG_ACTION_SIZE_BUFFER: @@ -2219,7 +2206,6 @@ asmlinkage int vprintk_emit(int facility, int level, { int printed_len; bool in_sched = false; - unsigned long flags; /* Suppress unimportant messages after panic happens */ if (unlikely(suppress_printk)) @@ -2233,9 +2219,7 @@ asmlinkage int vprintk_emit(int facility, int level, boot_delay_msec(level); printk_delay(); - printk_safe_enter_irqsave(flags); printed_len = vprintk_store(facility, level, dev_info, fmt, args); - printk_safe_exit_irqrestore(flags); /* If called from the scheduler, we can not call up(). */ if (!in_sched) { @@ -2664,9 +2648,9 @@ again: for (;;) { size_t ext_len = 0; + int handover; size_t len; - printk_safe_enter_irqsave(flags); skip: if (!prb_read_valid(prb, console_seq, &r)) break; @@ -2716,19 +2700,22 @@ skip: * were to occur on another CPU, it may wait for this one to * finish. This task can not be preempted if there is a * waiter waiting to take over. + * + * Interrupts are disabled because the hand over to a waiter + * must not be interrupted until the hand over is completed + * (@console_waiter is cleared). */ + printk_safe_enter_irqsave(flags); console_lock_spinning_enable(); stop_critical_timings(); /* don't trace print latency */ call_console_drivers(ext_text, ext_len, text, len); start_critical_timings(); - if (console_lock_spinning_disable_and_check()) { - printk_safe_exit_irqrestore(flags); - return; - } - + handover = console_lock_spinning_disable_and_check(); printk_safe_exit_irqrestore(flags); + if (handover) + return; if (do_cond_resched) cond_resched(); @@ -2745,8 +2732,6 @@ skip: * flush, no worries. */ retry = prb_read_valid(prb, console_seq, NULL); - printk_safe_exit_irqrestore(flags); - if (retry && console_trylock()) goto again; } @@ -2808,13 +2793,8 @@ void console_flush_on_panic(enum con_flush_mode mode) console_trylock(); console_may_schedule = 0; - if (mode == CONSOLE_REPLAY_ALL) { - unsigned long flags; - - printk_safe_enter_irqsave(flags); + if (mode == CONSOLE_REPLAY_ALL) console_seq = prb_first_valid_seq(prb); - printk_safe_exit_irqrestore(flags); - } console_unlock(); } @@ -3466,14 +3446,12 @@ bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog, struct printk_info info; unsigned int line_count; struct printk_record r; - unsigned long flags; size_t l = 0; bool ret = false; if (iter->cur_seq < min_seq) iter->cur_seq = min_seq; - printk_safe_enter_irqsave(flags); prb_rec_init_rd(&r, &info, line, size); /* Read text or count text lines? */ @@ -3494,7 +3472,6 @@ bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog, iter->cur_seq = r.info->seq + 1; ret = true; out: - printk_safe_exit_irqrestore(flags); if (len) *len = l; return ret; @@ -3526,7 +3503,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog, u64 min_seq = latched_seq_read_nolock(&clear_seq); struct printk_info info; struct printk_record r; - unsigned long flags; u64 seq; u64 next_seq; size_t len = 0; @@ -3539,7 +3515,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog, if (iter->cur_seq < min_seq) iter->cur_seq = min_seq; - printk_safe_enter_irqsave(flags); if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) { if (info.seq != iter->cur_seq) { /* messages are gone, move to first available one */ @@ -3548,10 +3523,8 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog, } /* last entry */ - if (iter->cur_seq >= iter->next_seq) { - printk_safe_exit_irqrestore(flags); + if (iter->cur_seq >= iter->next_seq) goto out; - } /* * Find first record that fits, including all following records, @@ -3583,7 +3556,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog, iter->next_seq = next_seq; ret = true; - printk_safe_exit_irqrestore(flags); out: if (len_out) *len_out = len; @@ -3601,12 +3573,8 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer); */ void kmsg_dump_rewind(struct kmsg_dump_iter *iter) { - unsigned long flags; - - printk_safe_enter_irqsave(flags); iter->cur_seq = latched_seq_read_nolock(&clear_seq); iter->next_seq = prb_next_seq(prb); - printk_safe_exit_irqrestore(flags); } EXPORT_SYMBOL_GPL(kmsg_dump_rewind); diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 94232186fccb..29c580dac93d 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -15,286 +15,9 @@ #include "internal.h" -/* - * In NMI and safe mode, printk() avoids taking locks. Instead, - * it uses an alternative implementation that temporary stores - * the strings into a per-CPU buffer. The content of the buffer - * is later flushed into the main ring buffer via IRQ work. - * - * The alternative implementation is chosen transparently - * by examining current printk() context mask stored in @printk_context - * per-CPU variable. - * - * The implementation allows to flush the strings also from another CPU. - * There are situations when we want to make sure that all buffers - * were handled or when IRQs are blocked. - */ - -#define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) - \ - sizeof(atomic_t) - \ - sizeof(atomic_t) - \ - sizeof(struct irq_work)) - -struct printk_safe_seq_buf { - atomic_t len; /* length of written data */ - atomic_t message_lost; - struct irq_work work; /* IRQ work that flushes the buffer */ - unsigned char buffer[SAFE_LOG_BUF_LEN]; -}; - -static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq); static DEFINE_PER_CPU(int, printk_context); -static DEFINE_RAW_SPINLOCK(safe_read_lock); - #ifdef CONFIG_PRINTK_NMI -static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq); -#endif - -/* Get flushed in a more safe context. */ -static void queue_flush_work(struct printk_safe_seq_buf *s) -{ - if (printk_percpu_data_ready()) - irq_work_queue(&s->work); -} - -/* - * Add a message to per-CPU context-dependent buffer. NMI and printk-safe - * have dedicated buffers, because otherwise printk-safe preempted by - * NMI-printk would have overwritten the NMI messages. - * - * The messages are flushed from irq work (or from panic()), possibly, - * from other CPU, concurrently with printk_safe_log_store(). Should this - * happen, printk_safe_log_store() will notice the buffer->len mismatch - * and repeat the write. - */ -static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s, - const char *fmt, va_list args) -{ - int add; - size_t len; - va_list ap; - -again: - len = atomic_read(&s->len); - - /* The trailing '\0' is not counted into len. */ - if (len >= sizeof(s->buffer) - 1) { - atomic_inc(&s->message_lost); - queue_flush_work(s); - return 0; - } - - /* - * Make sure that all old data have been read before the buffer - * was reset. This is not needed when we just append data. - */ - if (!len) - smp_rmb(); - - va_copy(ap, args); - add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap); - va_end(ap); - if (!add) - return 0; - - /* - * Do it once again if the buffer has been flushed in the meantime. - * Note that atomic_cmpxchg() is an implicit memory barrier that - * makes sure that the data were written before updating s->len. - */ - if (atomic_cmpxchg(&s->len, len, len + add) != len) - goto again; - - queue_flush_work(s); - return add; -} - -static inline void printk_safe_flush_line(const char *text, int len) -{ - /* - * Avoid any console drivers calls from here, because we may be - * in NMI or printk_safe context (when in panic). The messages - * must go only into the ring buffer at this stage. Consoles will - * get explicitly called later when a crashdump is not generated. - */ - printk_deferred("%.*s", len, text); -} - -/* printk part of the temporary buffer line by line */ -static int printk_safe_flush_buffer(const char *start, size_t len) -{ - const char *c, *end; - bool header; - - c = start; - end = start + len; - header = true; - - /* Print line by line. */ - while (c < end) { - if (*c == '\n') { - printk_safe_flush_line(start, c - start + 1); - start = ++c; - header = true; - continue; - } - - /* Handle continuous lines or missing new line. */ - if ((c + 1 < end) && printk_get_level(c)) { - if (header) { - c = printk_skip_level(c); - continue; - } - - printk_safe_flush_line(start, c - start); - start = c++; - header = true; - continue; - } - - header = false; - c++; - } - - /* Check if there was a partial line. Ignore pure header. */ - if (start < end && !header) { - static const char newline[] = KERN_CONT "\n"; - - printk_safe_flush_line(start, end - start); - printk_safe_flush_line(newline, strlen(newline)); - } - - return len; -} - -static void report_message_lost(struct printk_safe_seq_buf *s) -{ - int lost = atomic_xchg(&s->message_lost, 0); - - if (lost) - printk_deferred("Lost %d message(s)!\n", lost); -} - -/* - * Flush data from the associated per-CPU buffer. The function - * can be called either via IRQ work or independently. - */ -static void __printk_safe_flush(struct irq_work *work) -{ - struct printk_safe_seq_buf *s = - container_of(work, struct printk_safe_seq_buf, work); - unsigned long flags; - size_t len; - int i; - - /* - * The lock has two functions. First, one reader has to flush all - * available message to make the lockless synchronization with - * writers easier. Second, we do not want to mix messages from - * different CPUs. This is especially important when printing - * a backtrace. - */ - raw_spin_lock_irqsave(&safe_read_lock, flags); - - i = 0; -more: - len = atomic_read(&s->len); - - /* - * This is just a paranoid check that nobody has manipulated - * the buffer an unexpected way. If we printed something then - * @len must only increase. Also it should never overflow the - * buffer size. - */ - if ((i && i >= len) || len > sizeof(s->buffer)) { - const char *msg = "printk_safe_flush: internal error\n"; - - printk_safe_flush_line(msg, strlen(msg)); - len = 0; - } - - if (!len) - goto out; /* Someone else has already flushed the buffer. */ - - /* Make sure that data has been written up to the @len */ - smp_rmb(); - i += printk_safe_flush_buffer(s->buffer + i, len - i); - - /* - * Check that nothing has got added in the meantime and truncate - * the buffer. Note that atomic_cmpxchg() is an implicit memory - * barrier that makes sure that the data were copied before - * updating s->len. - */ - if (atomic_cmpxchg(&s->len, len, 0) != len) - goto more; - -out: - report_message_lost(s); - raw_spin_unlock_irqrestore(&safe_read_lock, flags); -} - -/** - * printk_safe_flush - flush all per-cpu nmi buffers. - * - * The buffers are flushed automatically via IRQ work. This function - * is useful only when someone wants to be sure that all buffers have - * been flushed at some point. - */ -void printk_safe_flush(void) -{ - int cpu; - - for_each_possible_cpu(cpu) { -#ifdef CONFIG_PRINTK_NMI - __printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work); -#endif - __printk_safe_flush(&per_cpu(safe_print_seq, cpu).work); - } -} - -/** - * printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system - * goes down. - * - * Similar to printk_safe_flush() but it can be called even in NMI context when - * the system goes down. It does the best effort to get NMI messages into - * the main ring buffer. - * - * Note that it could try harder when there is only one CPU online. - */ -void printk_safe_flush_on_panic(void) -{ - /* - * Make sure that we could access the safe buffers. - * Do not risk a double release when more CPUs are up. - */ - if (raw_spin_is_locked(&safe_read_lock)) { - if (num_online_cpus() > 1) - return; - - debug_locks_off(); - raw_spin_lock_init(&safe_read_lock); - } - - printk_safe_flush(); -} - -#ifdef CONFIG_PRINTK_NMI -/* - * Safe printk() for NMI context. It uses a per-CPU buffer to - * store the message. NMIs are not nested, so there is always only - * one writer running. But the buffer might get flushed from another - * CPU, so we need to be careful. - */ -static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args) -{ - struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq); - - return printk_safe_log_store(s, fmt, args); -} - void noinstr printk_nmi_enter(void) { this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET); @@ -309,9 +32,6 @@ void noinstr printk_nmi_exit(void) * Marks a code that might produce many messages in NMI context * and the risk of losing them is more critical than eventual * reordering. - * - * It has effect only when called in NMI context. Then printk() - * will store the messages into the main logbuf directly. */ void printk_nmi_direct_enter(void) { @@ -324,27 +44,8 @@ void printk_nmi_direct_exit(void) this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK); } -#else - -static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args) -{ - return 0; -} - #endif /* CONFIG_PRINTK_NMI */ -/* - * Lock-less printk(), to avoid deadlocks should the printk() recurse - * into itself. It uses a per-CPU buffer to store the message, just like - * NMI. - */ -static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args) -{ - struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq); - - return printk_safe_log_store(s, fmt, args); -} - /* Can be preempted by NMI. */ void __printk_safe_enter(void) { @@ -369,46 +70,18 @@ asmlinkage int vprintk(const char *fmt, va_list args) * Use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. */ - if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK)) { - unsigned long flags; + if (this_cpu_read(printk_context) & + (PRINTK_NMI_DIRECT_CONTEXT_MASK | + PRINTK_NMI_CONTEXT_MASK | + PRINTK_SAFE_CONTEXT_MASK)) { int len; - printk_safe_enter_irqsave(flags); len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args); - printk_safe_exit_irqrestore(flags); defer_console_output(); return len; } - /* Use extra buffer in NMI. */ - if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK) - return vprintk_nmi(fmt, args); - - /* Use extra buffer to prevent a recursion deadlock in safe mode. */ - if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK) - return vprintk_safe(fmt, args); - /* No obstacles. */ return vprintk_default(fmt, args); } EXPORT_SYMBOL(vprintk); - -void __init printk_safe_init(void) -{ - int cpu; - - for_each_possible_cpu(cpu) { - struct printk_safe_seq_buf *s; - - s = &per_cpu(safe_print_seq, cpu); - init_irq_work(&s->work, __printk_safe_flush); - -#ifdef CONFIG_PRINTK_NMI - s = &per_cpu(nmi_print_seq, cpu); - init_irq_work(&s->work, __printk_safe_flush); -#endif - } - - /* Flush pending messages that did not have scheduled IRQ works. */ - printk_safe_flush(); -} diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c index dae233c5f597..9813a983d024 100644 --- a/lib/nmi_backtrace.c +++ b/lib/nmi_backtrace.c @@ -75,12 +75,6 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask, touch_softlockup_watchdog(); } - /* - * Force flush any remote buffers that might be stuck in IRQ context - * and therefore could not run their irq_work. - */ - printk_safe_flush(); - clear_bit_unlock(0, &backtrace_flag); put_cpu(); } From 85e3e7fbbb720b9897fba9a99659e31cbd1c082e Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:57 +0206 Subject: [PATCH 4/7] printk: remove NMI tracking All NMI contexts are handled the same as the safe context: store the message and defer printing. There is no need to have special NMI context tracking for this. Using in_nmi() is enough. There are several parts of the kernel that are manually calling into the printk NMI context tracking in order to cause general printk deferred printing: arch/arm/kernel/smp.c arch/powerpc/kexec/crash.c kernel/trace/trace.c For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new function pair printk_deferred_enter/exit that explicitly achieves the same objective. For ftrace, remove the printk context manipulation completely. It was added in commit 03fc7f9c99c1 ("printk/nmi: Prevent deadlock when accessing the main log buffer in NMI"). The purpose was to enforce storing messages directly into the ring buffer even in NMI context. It really should have only modified the behavior in NMI context. There is no need for a special behavior any longer. All messages are always stored directly now. The console deferring is handled transparently in vprintk(). Signed-off-by: John Ogness [pmladek@suse.com: Remove special handling in ftrace.c completely. Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de --- arch/arm/kernel/smp.c | 4 ++-- arch/powerpc/kexec/crash.c | 2 +- include/linux/hardirq.h | 2 -- include/linux/printk.h | 31 +++++++++++++++++++------------ init/Kconfig | 5 ----- kernel/printk/internal.h | 8 -------- kernel/printk/printk_safe.c | 37 +------------------------------------ kernel/trace/trace.c | 2 -- 8 files changed, 23 insertions(+), 68 deletions(-) diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index c7bb168b0d97..842427ff2b3c 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -667,9 +667,9 @@ static void do_handle_IPI(int ipinr) break; case IPI_CPU_BACKTRACE: - printk_nmi_enter(); + printk_deferred_enter(); nmi_cpu_backtrace(get_irq_regs()); - printk_nmi_exit(); + printk_deferred_exit(); break; default: diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c index 0196d0c211ac..1070378c8e35 100644 --- a/arch/powerpc/kexec/crash.c +++ b/arch/powerpc/kexec/crash.c @@ -313,7 +313,7 @@ void default_machine_crash_shutdown(struct pt_regs *regs) int (*old_handler)(struct pt_regs *regs); /* Avoid hardlocking with irresponsive CPU holding logbuf_lock */ - printk_nmi_enter(); + printk_deferred_enter(); /* * This function is only called after the system diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 69bc86ea382c..76878b357ffa 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -116,7 +116,6 @@ extern void rcu_nmi_exit(void); do { \ lockdep_off(); \ arch_nmi_enter(); \ - printk_nmi_enter(); \ BUG_ON(in_nmi() == NMI_MASK); \ __preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ } while (0) @@ -135,7 +134,6 @@ extern void rcu_nmi_exit(void); do { \ BUG_ON(!in_nmi()); \ __preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \ - printk_nmi_exit(); \ arch_nmi_exit(); \ lockdep_on(); \ } while (0) diff --git a/include/linux/printk.h b/include/linux/printk.h index 719d919f9b67..a1379df43251 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -149,18 +149,6 @@ static inline __printf(1, 2) __cold void early_printk(const char *s, ...) { } #endif -#ifdef CONFIG_PRINTK_NMI -extern void printk_nmi_enter(void); -extern void printk_nmi_exit(void); -extern void printk_nmi_direct_enter(void); -extern void printk_nmi_direct_exit(void); -#else -static inline void printk_nmi_enter(void) { } -static inline void printk_nmi_exit(void) { } -static inline void printk_nmi_direct_enter(void) { } -static inline void printk_nmi_direct_exit(void) { } -#endif /* PRINTK_NMI */ - struct dev_printk_info; #ifdef CONFIG_PRINTK @@ -180,6 +168,16 @@ int printk(const char *fmt, ...); */ __printf(1, 2) __cold int printk_deferred(const char *fmt, ...); +extern void __printk_safe_enter(void); +extern void __printk_safe_exit(void); +/* + * The printk_deferred_enter/exit macros are available only as a hack for + * some code paths that need to defer all printk console printing. Interrupts + * must be disabled for the deferred duration. + */ +#define printk_deferred_enter __printk_safe_enter +#define printk_deferred_exit __printk_safe_exit + /* * Please don't use printk_ratelimit(), because it shares ratelimiting state * with all other unrelated printk_ratelimit() callsites. Instead use @@ -224,6 +222,15 @@ int printk_deferred(const char *s, ...) { return 0; } + +static inline void printk_deferred_enter(void) +{ +} + +static inline void printk_deferred_exit(void) +{ +} + static inline int printk_ratelimit(void) { return 0; diff --git a/init/Kconfig b/init/Kconfig index a61c92066c2e..9c0510693543 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1506,11 +1506,6 @@ config PRINTK very difficult to diagnose system problems, saying N here is strongly discouraged. -config PRINTK_NMI - def_bool y - depends on PRINTK - depends on HAVE_NMI - config BUG bool "BUG() support" if EXPERT default y diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 6cc35c5de890..b6d310c72fc9 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -6,12 +6,6 @@ #ifdef CONFIG_PRINTK -#define PRINTK_SAFE_CONTEXT_MASK 0x007ffffff -#define PRINTK_NMI_DIRECT_CONTEXT_MASK 0x008000000 -#define PRINTK_NMI_CONTEXT_MASK 0xff0000000 - -#define PRINTK_NMI_CONTEXT_OFFSET 0x010000000 - __printf(4, 0) int vprintk_store(int facility, int level, const struct dev_printk_info *dev_info, @@ -19,8 +13,6 @@ int vprintk_store(int facility, int level, __printf(1, 0) int vprintk_default(const char *fmt, va_list args); __printf(1, 0) int vprintk_deferred(const char *fmt, va_list args); -void __printk_safe_enter(void); -void __printk_safe_exit(void); bool printk_percpu_data_ready(void); diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 29c580dac93d..ef0f9a2044da 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -4,12 +4,9 @@ */ #include -#include -#include #include #include #include -#include #include #include @@ -17,35 +14,6 @@ static DEFINE_PER_CPU(int, printk_context); -#ifdef CONFIG_PRINTK_NMI -void noinstr printk_nmi_enter(void) -{ - this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET); -} - -void noinstr printk_nmi_exit(void) -{ - this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET); -} - -/* - * Marks a code that might produce many messages in NMI context - * and the risk of losing them is more critical than eventual - * reordering. - */ -void printk_nmi_direct_enter(void) -{ - if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK) - this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK); -} - -void printk_nmi_direct_exit(void) -{ - this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK); -} - -#endif /* CONFIG_PRINTK_NMI */ - /* Can be preempted by NMI. */ void __printk_safe_enter(void) { @@ -70,10 +38,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) * Use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. */ - if (this_cpu_read(printk_context) & - (PRINTK_NMI_DIRECT_CONTEXT_MASK | - PRINTK_NMI_CONTEXT_MASK | - PRINTK_SAFE_CONTEXT_MASK)) { + if (this_cpu_read(printk_context) || in_nmi()) { int len; len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index d23a09d3eb37..2f41311c61d7 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9647,7 +9647,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) tracing_off(); local_irq_save(flags); - printk_nmi_direct_enter(); /* Simulate the iterator */ trace_init_global_iter(&iter); @@ -9729,7 +9728,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) atomic_dec(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled); } atomic_dec(&dump_running); - printk_nmi_direct_exit(); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(ftrace_dump); From b371cbb584d843bc4194d0cd4ce5ecd19b0cf55f Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:58 +0206 Subject: [PATCH 5/7] printk: convert @syslog_lock to mutex @syslog_lock was a raw_spin_lock to simplify the transition of removing @logbuf_lock and the safe buffers. With that transition complete, and since all uses of @syslog_lock are within sleepable contexts, @syslog_lock can become a mutex. Note that until now register_console() would disable interrupts using irqsave, which implies that it may be called with interrupts disabled. And indeed, there is one possible call chain on parisc where this happens: handle_interruption(code=1) /* High-priority machine check (HPMC) */ pdc_console_restart() pdc_console_init_force() register_console() However, register_console() calls console_lock(), which might sleep. So it has never been allowed to call register_console() from an atomic context and the above call chain is a bug. Note that the removal of read_syslog_seq_irq() is slightly changing the behavior of SYSLOG_ACTION_READ by testing against a possibly outdated @seq value. However, the value of @seq could have changed after the test, so it is not a new window. A follow-up commit closes this window. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-6-john.ogness@linutronix.de --- kernel/printk/printk.c | 49 +++++++++++++++++------------------------- 1 file changed, 20 insertions(+), 29 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 219ad710a9e8..86f1258d08b0 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -356,7 +356,7 @@ enum log_flags { }; /* syslog_lock protects syslog_* variables and write access to clear_seq. */ -static DEFINE_RAW_SPINLOCK(syslog_lock); +static DEFINE_MUTEX(syslog_lock); #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); @@ -1497,9 +1497,9 @@ static int syslog_print(char __user *buf, int size) size_t n; size_t skip; - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); if (!prb_read_valid(prb, syslog_seq, &r)) { - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); break; } if (r.info->seq != syslog_seq) { @@ -1528,7 +1528,7 @@ static int syslog_print(char __user *buf, int size) syslog_partial += n; } else n = 0; - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); if (!n) break; @@ -1592,9 +1592,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear) } if (clear) { - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); latched_seq_write(&clear_seq, seq); - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); } kfree(text); @@ -1603,21 +1603,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear) static void syslog_clear(void) { - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); latched_seq_write(&clear_seq, prb_next_seq(prb)); - raw_spin_unlock_irq(&syslog_lock); -} - -/* Return a consistent copy of @syslog_seq. */ -static u64 read_syslog_seq_irq(void) -{ - u64 seq; - - raw_spin_lock_irq(&syslog_lock); - seq = syslog_seq; - raw_spin_unlock_irq(&syslog_lock); - - return seq; + mutex_unlock(&syslog_lock); } int do_syslog(int type, char __user *buf, int len, int source) @@ -1626,6 +1614,7 @@ int do_syslog(int type, char __user *buf, int len, int source) bool clear = false; static int saved_console_loglevel = LOGLEVEL_DEFAULT; int error; + u64 seq; error = check_syslog_permissions(type, source); if (error) @@ -1644,8 +1633,12 @@ int do_syslog(int type, char __user *buf, int len, int source) if (!access_ok(buf, len)) return -EFAULT; - error = wait_event_interruptible(log_wait, - prb_read_valid(prb, read_syslog_seq_irq(), NULL)); + /* Get a consistent copy of @syslog_seq. */ + mutex_lock(&syslog_lock); + seq = syslog_seq; + mutex_unlock(&syslog_lock); + + error = wait_event_interruptible(log_wait, prb_read_valid(prb, seq, NULL)); if (error) return error; error = syslog_print(buf, len); @@ -1693,10 +1686,10 @@ int do_syslog(int type, char __user *buf, int len, int source) break; /* Number of chars in the log buffer */ case SYSLOG_ACTION_SIZE_UNREAD: - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) { /* No unread messages. */ - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); return 0; } if (info.seq != syslog_seq) { @@ -1714,7 +1707,6 @@ int do_syslog(int type, char __user *buf, int len, int source) } else { bool time = syslog_partial ? syslog_time : printk_time; unsigned int line_count; - u64 seq; prb_for_each_info(syslog_seq, prb, seq, &info, &line_count) { @@ -1724,7 +1716,7 @@ int do_syslog(int type, char __user *buf, int len, int source) } error -= syslog_partial; } - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); break; /* Size of the log buffer */ case SYSLOG_ACTION_SIZE_BUFFER: @@ -2929,7 +2921,6 @@ static int try_enable_new_console(struct console *newcon, bool user_specified) */ void register_console(struct console *newcon) { - unsigned long flags; struct console *bcon = NULL; int err; @@ -3034,9 +3025,9 @@ void register_console(struct console *newcon) exclusive_console_stop_seq = console_seq; /* Get a consistent copy of @syslog_seq. */ - raw_spin_lock_irqsave(&syslog_lock, flags); + mutex_lock(&syslog_lock); console_seq = syslog_seq; - raw_spin_unlock_irqrestore(&syslog_lock, flags); + mutex_unlock(&syslog_lock); } console_unlock(); console_sysfs_notify(); From 8d909b2333f37e5da84a9e6a2cbe21f52be5f42a Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:59 +0206 Subject: [PATCH 6/7] printk: syslog: close window between wait and read Syslog's SYSLOG_ACTION_READ is supposed to block until the next syslog record can be read, and then it should read that record. However, because @syslog_lock is not held between waking up and reading the record, another reader could read the record first, thus causing SYSLOG_ACTION_READ to return with a value of 0, never having read _anything_. By holding @syslog_lock between waking up and reading, it can be guaranteed that SYSLOG_ACTION_READ blocks until it successfully reads a syslog record (or a real error occurs). Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-7-john.ogness@linutronix.de --- kernel/printk/printk.c | 55 +++++++++++++++++++++++++++--------------- 1 file changed, 36 insertions(+), 19 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 86f1258d08b0..65fffa6368c9 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1480,12 +1480,14 @@ static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size, return seq; } +/* The caller is responsible for making sure @size is greater than 0. */ static int syslog_print(char __user *buf, int size) { struct printk_info info; struct printk_record r; char *text; int len = 0; + u64 seq; text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL); if (!text) @@ -1493,15 +1495,35 @@ static int syslog_print(char __user *buf, int size) prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX); - while (size > 0) { + mutex_lock(&syslog_lock); + + /* + * Wait for the @syslog_seq record to be available. @syslog_seq may + * change while waiting. + */ + do { + seq = syslog_seq; + + mutex_unlock(&syslog_lock); + len = wait_event_interruptible(log_wait, prb_read_valid(prb, seq, NULL)); + mutex_lock(&syslog_lock); + + if (len) + goto out; + } while (syslog_seq != seq); + + /* + * Copy records that fit into the buffer. The above cycle makes sure + * that the first record is always available. + */ + do { size_t n; size_t skip; + int err; - mutex_lock(&syslog_lock); - if (!prb_read_valid(prb, syslog_seq, &r)) { - mutex_unlock(&syslog_lock); + if (!prb_read_valid(prb, syslog_seq, &r)) break; - } + if (r.info->seq != syslog_seq) { /* message is gone, move to next valid one */ syslog_seq = r.info->seq; @@ -1528,12 +1550,15 @@ static int syslog_print(char __user *buf, int size) syslog_partial += n; } else n = 0; - mutex_unlock(&syslog_lock); if (!n) break; - if (copy_to_user(buf, text + skip, n)) { + mutex_unlock(&syslog_lock); + err = copy_to_user(buf, text + skip, n); + mutex_lock(&syslog_lock); + + if (err) { if (!len) len = -EFAULT; break; @@ -1542,8 +1567,9 @@ static int syslog_print(char __user *buf, int size) len += n; size -= n; buf += n; - } - + } while (size); +out: + mutex_unlock(&syslog_lock); kfree(text); return len; } @@ -1614,7 +1640,6 @@ int do_syslog(int type, char __user *buf, int len, int source) bool clear = false; static int saved_console_loglevel = LOGLEVEL_DEFAULT; int error; - u64 seq; error = check_syslog_permissions(type, source); if (error) @@ -1632,15 +1657,6 @@ int do_syslog(int type, char __user *buf, int len, int source) return 0; if (!access_ok(buf, len)) return -EFAULT; - - /* Get a consistent copy of @syslog_seq. */ - mutex_lock(&syslog_lock); - seq = syslog_seq; - mutex_unlock(&syslog_lock); - - error = wait_event_interruptible(log_wait, prb_read_valid(prb, seq, NULL)); - if (error) - return error; error = syslog_print(buf, len); break; /* Read/clear last kernel messages */ @@ -1707,6 +1723,7 @@ int do_syslog(int type, char __user *buf, int len, int source) } else { bool time = syslog_partial ? syslog_time : printk_time; unsigned int line_count; + u64 seq; prb_for_each_info(syslog_seq, prb, seq, &info, &line_count) { From 26d1982fd17c2cac77f9cf764255362ccb28fe49 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Tue, 27 Jul 2021 10:09:39 +0200 Subject: [PATCH 7/7] lib/nmi_backtrace: Serialize even messages about idle CPUs The commit 55d6af1d66885059ffc2a ("lib/nmi_backtrace: explicitly serialize banner and regs") serialized backtraces from more CPUs using the re-entrant printk_printk_cpu lock. It was a preparation step for removing the obsolete nmi_safe buffers. The single-line messages about idle CPUs were not serialized against other CPUs and might appear in the middle of backtrace from another CPU, for example: [56394.590068] NMI backtrace for cpu 2 [56394.590069] CPU: 2 PID: 444 Comm: systemd-journal Not tainted 5.14.0-rc1-default+ #268 [56394.590071] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 [56394.590072] RIP: 0010:lock_is_held_type+0x0/0x120 [56394.590071] NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xb/0x10 [56394.590076] Code: a2 38 ff 0f 0b 8b 44 24 04 eb bd 48 8d ... [56394.590077] RSP: 0018:ffffab02c07c7e68 EFLAGS: 00000246 [56394.590079] RAX: 0000000000000000 RBX: ffff9a7bc0ec8a40 RCX: ffffffffaab8eb40 It might cause confusion what CPU the following lines belongs to and whether the backtraces are really serialized. Prevent the confusion and serialize also the single line message against other CPUs. Fixes: 55d6af1d66885059ffc2a ("lib/nmi_backtrace: explicitly serialize banner and regs") Reviewed-by: John Ogness Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210727080939.27193-1-pmladek@suse.com --- lib/nmi_backtrace.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c index 9813a983d024..f9e89001b52e 100644 --- a/lib/nmi_backtrace.c +++ b/lib/nmi_backtrace.c @@ -89,22 +89,22 @@ bool nmi_cpu_backtrace(struct pt_regs *regs) unsigned long flags; if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) { + /* + * Allow nested NMI backtraces while serializing + * against other CPUs. + */ + printk_cpu_lock_irqsave(flags); if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) { pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n", cpu, (void *)instruction_pointer(regs)); } else { - /* - * Allow nested NMI backtraces while serializing - * against other CPUs. - */ - printk_cpu_lock_irqsave(flags); pr_warn("NMI backtrace for cpu %d\n", cpu); if (regs) show_regs(regs); else dump_stack(); - printk_cpu_unlock_irqrestore(flags); } + printk_cpu_unlock_irqrestore(flags); cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); return true; }