path: root/samples
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authorSteven Rostedt (Red Hat) <>2015-07-07 15:05:03 -0400
committerSteven Rostedt <>2015-07-08 11:53:45 -0400
commit6224beb12e190ff11f3c7d4bf50cb2922878f600 (patch)
tree1397e410bb96d75fe5de6689145e6a8ea250a7c5 /samples
parentd770e558e21961ad6cfdf0ff7df0eb5d7d4f0754 (diff)
tracing: Have branch tracer use recursive field of task struct
Fengguang Wu's tests triggered a bug in the branch tracer's start up test when CONFIG_DEBUG_PREEMPT set. This was because that config adds some debug logic in the per cpu field, which calls back into the branch tracer. The branch tracer has its own recursive checks, but uses a per cpu variable to implement it. If retrieving the per cpu variable calls back into the branch tracer, you can see how things will break. Instead of using a per cpu variable, use the trace_recursion field of the current task struct. Simply set a bit when entering the branch tracing and clear it when leaving. If the bit is set on entry, just don't do the tracing. There's also the case with lockdep, as the local_irq_save() called before the recursion can also trigger code that can call back into the function. Changing that to a raw_local_irq_save() will protect that as well. This prevents the recursion and the inevitable crash that follows. Link: Cc: # 3.10+ Reported-by: Fengguang Wu <> Tested-by: Fengguang Wu <> Signed-off-by: Steven Rostedt <>
Diffstat (limited to 'samples')
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