* uretprobe occasionally fires twice
@ 2017-08-08 18:56 Benjamin King
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From: Benjamin King @ 2017-08-08 18:56 UTC (permalink / raw)
To: linux-perf-users
Hi,
I have placed a uprobe and a uretprobe on the same function in libc. When
perf record'ing a larger test where the function is called from multiple
threads, I can occasionally see the following sequence of events in a 'perf
script':
1) uretprobe fires
2) uprobe fires
3) uretprobe fires again
More specifically, I am tracing libc's realloc. Since I trace the size of
the memory in question, I think that the uretprobe in 1) is called at
function entry.
This only happens occasionally and I unfortunately I could not reproduce it
with a small testcase yet.
'perf script' prints two warnings:
* Processed 17216221 events and lost 2 chunks!
* 114 out of order events recorded.
Could this explain the duplicated output? Are there other known circumstances
where a uretprobe could be unreliable in some way?
Cheers,
Benjamin
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