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printk changes for 5.11

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Merge tag 'printk-for-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Finally allow parallel writes and reads into/from the lockless
   ringbuffer. But it is not a complete solution. Readers are still
   serialized against each other. And nested writes are still prevented
   by printk_safe per-CPU buffers.

 - Use ttynull as the ultimate fallback for /dev/console.

 - Officially allow disabling console output by using console="" or
   console=null

 - A few code cleanups

* tag 'printk-for-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk: remove logbuf_lock writer-protection of ringbuffer
  printk: inline log_output(),log_store() in vprintk_store()
  printk: remove obsolete dead assignment
  printk/console: Allow to disable console output by using console="" or console=null
  init/console: Use ttynull as a fallback when there is no console
  printk: ringbuffer: Reference text_data_ring directly in callees.
This commit is contained in:
Linus Torvalds 2020-12-16 10:45:11 -08:00
commit d3eb52113d
7 changed files with 202 additions and 139 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
drivers/tty/Kconfig
View File

@ -401,20 +401,6 @@ config MIPS_EJTAG_FDC_KGDB_CHAN
help
FDC channel number to use for KGDB.
config NULL_TTY
tristate "NULL TTY driver"
help
Say Y here if you want a NULL TTY which simply discards messages.
This is useful to allow userspace applications which expect a console
device to work without modifications even when no console is
available or desired.
In order to use this driver, you should redirect the console to this
TTY, or boot the kernel with console=ttynull.
If unsure, say N.
config TRACE_ROUTER
tristate "Trace data router for MIPI P1149.7 cJTAG standard"
depends on TRACE_SINK

3
drivers/tty/Makefile
View File

@ -2,7 +2,7 @@
obj-$(CONFIG_TTY) += tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
tty_buffer.o tty_port.o tty_mutex.o \
tty_ldsem.o tty_baudrate.o tty_jobctrl.o \
n_null.o
n_null.o ttynull.o
obj-$(CONFIG_LEGACY_PTYS) += pty.o
obj-$(CONFIG_UNIX98_PTYS) += pty.o
obj-$(CONFIG_AUDIT) += tty_audit.o
@ -25,7 +25,6 @@ obj-$(CONFIG_ISI) += isicom.o
obj-$(CONFIG_MOXA_INTELLIO) += moxa.o
obj-$(CONFIG_MOXA_SMARTIO) += mxser.o
obj-$(CONFIG_NOZOMI) += nozomi.o
obj-$(CONFIG_NULL_TTY) += ttynull.o
obj-$(CONFIG_ROCKETPORT) += rocket.o
obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o
obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o

18
drivers/tty/ttynull.c
View File

@ -2,6 +2,13 @@
/*
* Copyright (C) 2019 Axis Communications AB
*
* The console is useful for userspace applications which expect a console
* device to work without modifications even when no console is available
* or desired.
*
* In order to use this driver, you should redirect the console to this
* TTY, or boot the kernel with console=ttynull.
*
* Based on ttyprintk.c:
* Copyright (C) 2010 Samo Pogacnik
*/
@ -59,6 +66,17 @@ static struct console ttynull_console = {
.device = ttynull_device,
};
void __init register_ttynull_console(void)
{
if (!ttynull_driver)
return;
if (add_preferred_console(ttynull_console.name, 0, NULL))
return;
register_console(&ttynull_console);
}
static int __init ttynull_init(void)
{
struct tty_driver *driver;

3
include/linux/console.h
View File

@ -186,9 +186,12 @@ extern int braille_register_console(struct console *, int index,
extern int braille_unregister_console(struct console *);
#ifdef CONFIG_TTY
extern void console_sysfs_notify(void);
extern void register_ttynull_console(void);
#else
static inline void console_sysfs_notify(void)
{ }
static inline void register_ttynull_console(void)
{ }
#endif
extern bool console_suspend_enabled;

8
init/main.c
View File

@ -1480,9 +1480,15 @@ void __init console_on_rootfs(void)
struct file *file = filp_open("/dev/console", O_RDWR, 0);
if (IS_ERR(file)) {
pr_err("Warning: unable to open an initial console.\n");
pr_err("Warning: unable to open an initial console. Fallback to ttynull.\n");
register_ttynull_console();
file = filp_open("/dev/console", O_RDWR, 0);
if (IS_ERR(file)) {
pr_err("Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process!\n");
return;
}
}
init_dup(file);
init_dup(file);
init_dup(file);

263
kernel/printk/printk.c
View File

@ -491,52 +491,6 @@ static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
*trunc_msg_len = 0;
}
/* insert record into the buffer, discard old ones, update heads */
static int log_store(u32 caller_id, int facility, int level,
enum log_flags flags, u64 ts_nsec,
const struct dev_printk_info *dev_info,
const char *text, u16 text_len)
{
struct prb_reserved_entry e;
struct printk_record r;
u16 trunc_msg_len = 0;
prb_rec_init_wr(&r, text_len);
if (!prb_reserve(&e, prb, &r)) {
/* truncate the message if it is too long for empty buffer */
truncate_msg(&text_len, &trunc_msg_len);
prb_rec_init_wr(&r, text_len + trunc_msg_len);
/* survive when the log buffer is too small for trunc_msg */
if (!prb_reserve(&e, prb, &r))
return 0;
}
/* fill message */
memcpy(&r.text_buf[0], text, text_len);
if (trunc_msg_len)
memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
r.info->text_len = text_len + trunc_msg_len;
r.info->facility = facility;
r.info->level = level & 7;
r.info->flags = flags & 0x1f;
if (ts_nsec > 0)
r.info->ts_nsec = ts_nsec;
else
r.info->ts_nsec = local_clock();
r.info->caller_id = caller_id;
if (dev_info)
memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
/* A message without a trailing newline can be continued. */
if (!(flags & LOG_NEWLINE))
prb_commit(&e);
else
prb_final_commit(&e);
return (text_len + trunc_msg_len);
}
int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
static int syslog_action_restricted(int type)
@ -741,7 +695,6 @@ static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
if (LOG_FACILITY(u) != 0)
facility = LOG_FACILITY(u);
endp++;
len -= endp - line;
line = endp;
}
}
@ -1172,7 +1125,7 @@ void __init setup_log_buf(int early)
new_descs, ilog2(new_descs_count),
new_infos);
logbuf_lock_irqsave(flags);
printk_safe_enter_irqsave(flags);
log_buf_len = new_log_buf_len;
log_buf = new_log_buf;
@ -1189,7 +1142,7 @@ void __init setup_log_buf(int early)
*/
prb = &printk_rb_dynamic;
logbuf_unlock_irqrestore(flags);
printk_safe_exit_irqrestore(flags);
if (seq != prb_next_seq(&printk_rb_static)) {
pr_err("dropped %llu messages\n",
@ -1907,75 +1860,117 @@ static inline u32 printk_caller_id(void)
0x80000000 + raw_smp_processor_id();
}
static size_t log_output(int facility, int level, enum log_flags lflags,
const struct dev_printk_info *dev_info,
char *text, size_t text_len)
/**
* parse_prefix - Parse level and control flags.
*
* @text: The terminated text message.
* @level: A pointer to the current level value, will be updated.
* @lflags: A pointer to the current log flags, will be updated.
*
* @level may be NULL if the caller is not interested in the parsed value.
* Otherwise the variable pointed to by @level must be set to
* LOGLEVEL_DEFAULT in order to be updated with the parsed value.
*
* @lflags may be NULL if the caller is not interested in the parsed value.
* Otherwise the variable pointed to by @lflags will be OR'd with the parsed
* value.
*
* Return: The length of the parsed level and control flags.
*/
static u16 parse_prefix(char *text, int *level, enum log_flags *lflags)
{
const u32 caller_id = printk_caller_id();
u16 prefix_len = 0;
int kern_level;
if (lflags & LOG_CONT) {
struct prb_reserved_entry e;
struct printk_record r;
while (*text) {
kern_level = printk_get_level(text);
if (!kern_level)
break;
prb_rec_init_wr(&r, text_len);
if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
memcpy(&r.text_buf[r.info->text_len], text, text_len);
r.info->text_len += text_len;
if (lflags & LOG_NEWLINE) {
r.info->flags |= LOG_NEWLINE;
prb_final_commit(&e);
} else {
prb_commit(&e);
}
return text_len;
}
switch (kern_level) {
case '0' ... '7':
if (level && *level == LOGLEVEL_DEFAULT)
*level = kern_level - '0';
break;
case 'c': /* KERN_CONT */
if (lflags)
*lflags |= LOG_CONT;
}
/* Store it in the record log */
return log_store(caller_id, facility, level, lflags, 0,
dev_info, text, text_len);
prefix_len += 2;
text += 2;
}
return prefix_len;
}
/* Must be called under logbuf_lock. */
static u16 printk_sprint(char *text, u16 size, int facility, enum log_flags *lflags,
const char *fmt, va_list args)
{
u16 text_len;
text_len = vscnprintf(text, size, fmt, args);
/* Mark and strip a trailing newline. */
if (text_len && text[text_len - 1] == '\n') {
text_len--;
*lflags |= LOG_NEWLINE;
}
/* Strip log level and control flags. */
if (facility == 0) {
u16 prefix_len;
prefix_len = parse_prefix(text, NULL, NULL);
if (prefix_len) {
text_len -= prefix_len;
memmove(text, text + prefix_len, text_len);
}
}
return text_len;
}
__printf(4, 0)
int vprintk_store(int facility, int level,
const struct dev_printk_info *dev_info,
const char *fmt, va_list args)
{
static char textbuf[LOG_LINE_MAX];
char *text = textbuf;
size_t text_len;
const u32 caller_id = printk_caller_id();
struct prb_reserved_entry e;
enum log_flags lflags = 0;
struct printk_record r;
u16 trunc_msg_len = 0;
char prefix_buf[8];
u16 reserve_size;
va_list args2;
u16 text_len;
u64 ts_nsec;
/*
* The printf needs to come first; we need the syslog
* prefix which might be passed-in as a parameter.
* Since the duration of printk() can vary depending on the message
* and state of the ringbuffer, grab the timestamp now so that it is
* close to the call of printk(). This provides a more deterministic
* timestamp with respect to the caller.
*/
text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
ts_nsec = local_clock();
/* mark and strip a trailing newline */
if (text_len && text[text_len-1] == '\n') {
text_len--;
lflags |= LOG_NEWLINE;
}
/*
* 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
* later the vscnprintf() into the reserved buffer has room for the
* terminating '\0', which is not counted by vsnprintf().
*/
va_copy(args2, args);
reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
va_end(args2);
/* strip kernel syslog prefix and extract log level or control flags */
if (facility == 0) {
int kern_level;
if (reserve_size > LOG_LINE_MAX)
reserve_size = LOG_LINE_MAX;
while ((kern_level = printk_get_level(text)) != 0) {
switch (kern_level) {
case '0' ... '7':
if (level == LOGLEVEL_DEFAULT)
level = kern_level - '0';
break;
case 'c': /* KERN_CONT */
lflags |= LOG_CONT;
}
text_len -= 2;
text += 2;
}
}
/* Extract log level or control flags. */
if (facility == 0)
parse_prefix(&prefix_buf[0], &level, &lflags);
if (level == LOGLEVEL_DEFAULT)
level = default_message_loglevel;
@ -1983,7 +1978,59 @@ int vprintk_store(int facility, int level,
if (dev_info)
lflags |= LOG_NEWLINE;
return log_output(facility, level, lflags, dev_info, text, text_len);
if (lflags & LOG_CONT) {
prb_rec_init_wr(&r, reserve_size);
if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
facility, &lflags, fmt, args);
r.info->text_len += text_len;
if (lflags & LOG_NEWLINE) {
r.info->flags |= LOG_NEWLINE;
prb_final_commit(&e);
} else {
prb_commit(&e);
}
return text_len;
}
}
/*
* Explicitly initialize the record before every prb_reserve() call.
* prb_reserve_in_last() and prb_reserve() purposely invalidate the
* structure when they fail.
*/
prb_rec_init_wr(&r, reserve_size);
if (!prb_reserve(&e, prb, &r)) {
/* truncate the message if it is too long for empty buffer */
truncate_msg(&reserve_size, &trunc_msg_len);
prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
if (!prb_reserve(&e, prb, &r))
return 0;
}
/* fill message */
text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &lflags, fmt, args);
if (trunc_msg_len)
memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
r.info->text_len = text_len + trunc_msg_len;
r.info->facility = facility;
r.info->level = level & 7;
r.info->flags = lflags & 0x1f;
r.info->ts_nsec = ts_nsec;
r.info->caller_id = caller_id;
if (dev_info)
memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
/* A message without a trailing newline can be continued. */
if (!(lflags & LOG_NEWLINE))
prb_commit(&e);
else
prb_final_commit(&e);
return (text_len + trunc_msg_len);
}
asmlinkage int vprintk_emit(int facility, int level,
@ -2006,10 +2053,9 @@ asmlinkage int vprintk_emit(int facility, int level,
boot_delay_msec(level);
printk_delay();
/* This stops the holder of console_sem just where we want him */
logbuf_lock_irqsave(flags);
printk_safe_enter_irqsave(flags);
printed_len = vprintk_store(facility, level, dev_info, fmt, args);
logbuf_unlock_irqrestore(flags);
printk_safe_exit_irqrestore(flags);
/* If called from the scheduler, we can not call up(). */
if (!in_sched) {
@ -2189,8 +2235,15 @@ static int __init console_setup(char *str)
char *s, *options, *brl_options = NULL;
int idx;
if (str[0] == 0)
/*
* console="" or console=null have been suggested as a way to
* disable console output. Use ttynull that has been created
* for exacly this purpose.
*/
if (str[0] == 0 || strcmp(str, "null") == 0) {
__add_preferred_console("ttynull", 0, NULL, NULL, true);
return 1;
}
if (_braille_console_setup(&str, &brl_options))
return 1;

32
kernel/printk/printk_ringbuffer.c
View File

@ -559,11 +559,12 @@ static void desc_make_reusable(struct prb_desc_ring *desc_ring,
* on error the caller can re-load the tail lpos to determine the situation.
*/
static bool data_make_reusable(struct printk_ringbuffer *rb,
struct prb_data_ring *data_ring,
unsigned long lpos_begin,
unsigned long lpos_end,
unsigned long *lpos_out)
{
struct prb_data_ring *data_ring = &rb->text_data_ring;
struct prb_desc_ring *desc_ring = &rb->desc_ring;
struct prb_data_block *blk;
enum desc_state d_state;
@ -625,10 +626,9 @@ static bool data_make_reusable(struct printk_ringbuffer *rb,
* descriptors into the reusable state if the tail is pushed beyond
* their associated data block.
*/
static bool data_push_tail(struct printk_ringbuffer *rb,
struct prb_data_ring *data_ring,
unsigned long lpos)
static bool data_push_tail(struct printk_ringbuffer *rb, unsigned long lpos)
{
struct prb_data_ring *data_ring = &rb->text_data_ring;
unsigned long tail_lpos_new;
unsigned long tail_lpos;
unsigned long next_lpos;
@ -669,8 +669,7 @@ static bool data_push_tail(struct printk_ringbuffer *rb,
* Make all descriptors reusable that are associated with
* data blocks before @lpos.
*/
if (!data_make_reusable(rb, data_ring, tail_lpos, lpos,
&next_lpos)) {
if (!data_make_reusable(rb, tail_lpos, lpos, &next_lpos)) {
/*
* 1. Guarantee the block ID loaded in
* data_make_reusable() is performed before
@ -807,7 +806,7 @@ static bool desc_push_tail(struct printk_ringbuffer *rb,
* data blocks once their associated descriptor is gone.
*/
if (!data_push_tail(rb, &rb->text_data_ring, desc.text_blk_lpos.next))
if (!data_push_tail(rb, desc.text_blk_lpos.next))
return false;
/*
@ -1019,10 +1018,10 @@ static unsigned long get_next_lpos(struct prb_data_ring *data_ring,
* if necessary. This function also associates the data block with
* a specified descriptor.
*/
static char *data_alloc(struct printk_ringbuffer *rb,
struct prb_data_ring *data_ring, unsigned int size,
static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size,
struct prb_data_blk_lpos *blk_lpos, unsigned long id)
{
struct prb_data_ring *data_ring = &rb->text_data_ring;
struct prb_data_block *blk;
unsigned long begin_lpos;
unsigned long next_lpos;
@ -1041,7 +1040,7 @@ static char *data_alloc(struct printk_ringbuffer *rb,
do {
next_lpos = get_next_lpos(data_ring, begin_lpos, size);
if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring))) {
if (!data_push_tail(rb, next_lpos - DATA_SIZE(data_ring))) {
/* Failed to allocate, specify a data-less block. */
blk_lpos->begin = FAILED_LPOS;
blk_lpos->next = FAILED_LPOS;
@ -1100,10 +1099,10 @@ static char *data_alloc(struct printk_ringbuffer *rb,
* Return a pointer to the beginning of the entire data buffer or NULL on
* failure.
*/
static char *data_realloc(struct printk_ringbuffer *rb,
struct prb_data_ring *data_ring, unsigned int size,
static char *data_realloc(struct printk_ringbuffer *rb, unsigned int size,
struct prb_data_blk_lpos *blk_lpos, unsigned long id)
{
struct prb_data_ring *data_ring = &rb->text_data_ring;
struct prb_data_block *blk;
unsigned long head_lpos;
unsigned long next_lpos;
@ -1130,7 +1129,7 @@ static char *data_realloc(struct printk_ringbuffer *rb,
return &blk->data[0];
}
if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring)))
if (!data_push_tail(rb, next_lpos - DATA_SIZE(data_ring)))
return NULL;
/* The memory barrier involvement is the same as data_alloc:A. */
@ -1395,7 +1394,7 @@ bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer
if (r->text_buf_size > max_size)
goto fail;
r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size,
r->text_buf = data_alloc(rb, r->text_buf_size,
&d->text_blk_lpos, id);
} else {
if (!get_data(&rb->text_data_ring, &d->text_blk_lpos, &data_size))
@ -1419,7 +1418,7 @@ bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer
if (r->text_buf_size > max_size)
goto fail;
r->text_buf = data_realloc(rb, &rb->text_data_ring, r->text_buf_size,
r->text_buf = data_realloc(rb, r->text_buf_size,
&d->text_blk_lpos, id);
}
if (r->text_buf_size && !r->text_buf)
@ -1547,8 +1546,7 @@ bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
if (info->seq > 0)
desc_make_final(desc_ring, DESC_ID(id - 1));
r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size,
&d->text_blk_lpos, id);
r->text_buf = data_alloc(rb, r->text_buf_size, &d->text_blk_lpos, id);
/* If text data allocation fails, a data-less record is committed. */
if (r->text_buf_size && !r->text_buf) {
prb_commit(e);