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This includes two fixes

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- Bring back context level recursive protection in ring buffer.
    The simpler counter protection failed, due to a path when
    tracing with trace_clock_global() as it could not be reentrant
    and depended on the ring buffer recursive protection to keep that
    from happening.
 
  - Prevent branch profiling when FORTIFY_SOURCE is enabled. It causes
    50 - 60 MB in warning messages. Branch profiling should never be
    run on production systems, so there's no reason that it needs to
    be enabled with FORTIFY_SOURCE.
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Merge tag 'trace-v4.15-rc4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:

 - Bring back context level recursive protection in ring buffer.

   The simpler counter protection failed, due to a path when tracing
   with trace_clock_global() as it could not be reentrant and depended
   on the ring buffer recursive protection to keep that from happening.

 - Prevent branch profiling when FORTIFY_SOURCE is enabled.

   It causes 50 - 60 MB in warning messages. Branch profiling should
   never be run on production systems, so there's no reason that it
   needs to be enabled with FORTIFY_SOURCE.

* tag 'trace-v4.15-rc4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Prevent PROFILE_ALL_BRANCHES when FORTIFY_SOURCE=y
  ring-buffer: Bring back context level recursive checks
This commit is contained in:
Linus Torvalds 2018-01-16 12:09:36 -08:00
commit 921d4f67bf
2 changed files with 46 additions and 18 deletions
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2
kernel/trace/Kconfig
View File

@ -355,7 +355,7 @@ config PROFILE_ANNOTATED_BRANCHES
on if you need to profile the system's use of these macros.
config PROFILE_ALL_BRANCHES
bool "Profile all if conditionals"
bool "Profile all if conditionals" if !FORTIFY_SOURCE
select TRACE_BRANCH_PROFILING
help
This tracer profiles all branch conditions. Every if ()

62
kernel/trace/ring_buffer.c
View File

@ -2534,29 +2534,59 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
* The lock and unlock are done within a preempt disable section.
* The current_context per_cpu variable can only be modified
* by the current task between lock and unlock. But it can
* be modified more than once via an interrupt. There are four
* different contexts that we need to consider.
* be modified more than once via an interrupt. To pass this
* information from the lock to the unlock without having to
* access the 'in_interrupt()' functions again (which do show
* a bit of overhead in something as critical as function tracing,
* we use a bitmask trick.
*
* Normal context.
* SoftIRQ context
* IRQ context
* NMI context
* bit 0 = NMI context
* bit 1 = IRQ context
* bit 2 = SoftIRQ context
* bit 3 = normal context.
*
* If for some reason the ring buffer starts to recurse, we
* only allow that to happen at most 4 times (one for each
* context). If it happens 5 times, then we consider this a
* recusive loop and do not let it go further.
* This works because this is the order of contexts that can
* preempt other contexts. A SoftIRQ never preempts an IRQ
* context.
*
* When the context is determined, the corresponding bit is
* checked and set (if it was set, then a recursion of that context
* happened).
*
* On unlock, we need to clear this bit. To do so, just subtract
* 1 from the current_context and AND it to itself.
*
* (binary)
* 101 - 1 = 100
* 101 & 100 = 100 (clearing bit zero)
*
* 1010 - 1 = 1001
* 1010 & 1001 = 1000 (clearing bit 1)
*
* The least significant bit can be cleared this way, and it
* just so happens that it is the same bit corresponding to
* the current context.
*/
static __always_inline int
trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
{
if (cpu_buffer->current_context >= 4)
unsigned int val = cpu_buffer->current_context;
unsigned long pc = preempt_count();
int bit;
if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
bit = RB_CTX_NORMAL;
else
bit = pc & NMI_MASK ? RB_CTX_NMI :
pc & HARDIRQ_MASK ? RB_CTX_IRQ :
pc & SOFTIRQ_OFFSET ? 2 : RB_CTX_SOFTIRQ;
if (unlikely(val & (1 << bit)))
return 1;
cpu_buffer->current_context++;
/* Interrupts must see this update */
barrier();
val |= (1 << bit);
cpu_buffer->current_context = val;
return 0;
}
@ -2564,9 +2594,7 @@ trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
static __always_inline void
trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
{
/* Don't let the dec leak out */
barrier();
cpu_buffer->current_context--;
cpu_buffer->current_context &= cpu_buffer->current_context - 1;
}
/**