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Fengguang Wu discovered a crash that happened to be because of the branch

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tracer (traces unlikely and likely branches) when enabled with certain
 debug options.
 
 What happened was that various debug options like lockdep and DEBUG_PREEMPT
 can cause parts of the branch tracer to recurse outside its recursion
 protection. In fact, part of its recursion protection used these features
 that caused the lockup. This cleans up the code a little and makes the
 recursion protection a bit more robust.
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Merge tag 'trace-v4.2-rc1-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fix from Steven Rostedt:
 "Fengguang Wu discovered a crash that happened to be because of the
  branch tracer (traces unlikely and likely branches) when enabled with
  certain debug options.

  What happened was that various debug options like lockdep and
  DEBUG_PREEMPT can cause parts of the branch tracer to recurse outside
  its recursion protection.  In fact, part of its recursion protection
  used these features that caused the lockup.  This cleans up the code a
  little and makes the recursion protection a bit more robust"

* tag 'trace-v4.2-rc1-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Have branch tracer use recursive field of task struct
This commit is contained in:
Linus Torvalds 2015-07-15 11:14:10 -07:00
commit 7558009751
2 changed files with 11 additions and 7 deletions
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1
kernel/trace/trace.h
View File

@ -444,6 +444,7 @@ enum {
TRACE_CONTROL_BIT,
TRACE_BRANCH_BIT,
/*
* Abuse of the trace_recursion.
* As we need a way to maintain state if we are tracing the function

17
kernel/trace/trace_branch.c
View File

@ -36,9 +36,12 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
struct trace_branch *entry;
struct ring_buffer *buffer;
unsigned long flags;
int cpu, pc;
int pc;
const char *p;
if (current->trace_recursion & TRACE_BRANCH_BIT)
return;
/*
* I would love to save just the ftrace_likely_data pointer, but
* this code can also be used by modules. Ugly things can happen
@ -49,10 +52,10 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
if (unlikely(!tr))
return;
local_irq_save(flags);
cpu = raw_smp_processor_id();
data = per_cpu_ptr(tr->trace_buffer.data, cpu);
if (atomic_inc_return(&data->disabled) != 1)
raw_local_irq_save(flags);
current->trace_recursion |= TRACE_BRANCH_BIT;
data = this_cpu_ptr(tr->trace_buffer.data);
if (atomic_read(&data->disabled))
goto out;
pc = preempt_count();
@ -81,8 +84,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
__buffer_unlock_commit(buffer, event);
out:
atomic_dec(&data->disabled);
local_irq_restore(flags);
current->trace_recursion &= ~TRACE_BRANCH_BIT;
raw_local_irq_restore(flags);
}
static inline