[cfe-users] TSAN and pthread_setcancelstate()

Rainer Gerhards via cfe-users cfe-users at lists.llvm.org
Sat Dec 30 02:57:52 PST 2017


Adding to my own question:

I have tried to use __attribute__((no_sanitize("thread"))) and
blacklisting to work around the issue, but without any success.

Details in commit
https://github.com/rgerhards/rsyslog/commit/8e7625a5b21924518739acf17712f028c4c25241

This has now actually become a blocker for me in regard to adoption of
TSAN. Any help would be highly appreciated!

Thanks and happy new year,
Rainer

2017-12-29 19:01 GMT+01:00 Rainer Gerhards <rgerhards at hq.adiscon.com>:
> Hi all,
>
> I hope this is the right list for my question. If not, please accept
> my apologies -- in that case I would also appreciate if you could tell
> me the right place to ask.
>
> I am using TSAN together with clang (3,4,5) on Linux (in this Case
> Ubuntu 16.04). It works great, but I always get race reports (sample
> after my sig) on pthread_setcancelstate(). The POSIX doc states that
> it sets the cancellation state for the *current thread* so there
> should be no cross-thread data races. To validate this, I have also
> checked the GNU libc and pthread implemenation and the both access
> thread-local storage.
>
> So I wonder what I may be doing wrong and most importantly what I can
> decently do in order to get rid of the TSAN message (false positive?).
> I know I can disable TSAN on a function basis, but that is a but
> clumpsy as I do not want to disable if for more but the
> pthread_setcancelstate. In an extreme, I probably need to move it to
> an inline wrapper, but I don't consider this to be really clean.
>
> Any advise, especially on the root cause, would be much appreciated.
> It makes me kind of nervous not understanding why this happens at
> all...
>
> Thanks in advance,
> Rainer
>
> Sample Report:
> WARNING: ThreadSanitizer: data race (pid=103016)
>   Write of size 1 at 0x7c0000000000 by main thread:
>     #0 pthread_setcancelstate <null> (rsyslogd+0x00000043a830)
>     #1 qqueueEnqMsg /home/rger/proj/rsyslog/runtime/queue.c:3039:3
> (rsyslogd+0x0000005a20d9)
>     #2 submitMsg2 /home/rger/proj/rsyslog/tools/rsyslogd.c:1015:2
> (rsyslogd+0x0000004b08b0)
>     #3 logmsgInternal_doWrite
> /home/rger/proj/rsyslog/tools/rsyslogd.c:864:3
> (rsyslogd+0x0000004b0cc0)
>     #4 processImInternal
> /home/rger/proj/rsyslog/tools/rsyslogd.c:1566:4
> (rsyslogd+0x0000004b0c4b)
>     #5 mainloop /home/rger/proj/rsyslog/tools/rsyslogd.c:1787:3
> (rsyslogd+0x0000004b2df5)
>     #6 main /home/rger/proj/rsyslog/tools/rsyslogd.c:1965:2
> (rsyslogd+0x0000004b15cf)
>
>   Previous write of size 1 at 0x7c0000000000 by thread T1:
>     #0 pthread_setcancelstate <null> (rsyslogd+0x00000043a830)
>     #1 ConsumerReg /home/rger/proj/rsyslog/runtime/queue.c:2029:2
> (rsyslogd+0x00000059e6f9)
>     #2 wtiWorker /home/rger/proj/rsyslog/runtime/wti.c:366:14
> (rsyslogd+0x000000591683)
>     #3 wtpWorker /home/rger/proj/rsyslog/runtime/wtp.c:415:2
> (rsyslogd+0x00000058e371)
>
>   Thread T1 'rs:main Q[DA]:R' (tid=103049, running) created by main thread at:
>     #0 pthread_create <null> (rsyslogd+0x00000042dc76)
>     #1 wtpStartWrkr /home/rger/proj/rsyslog/runtime/wtp.c:464:11
> (rsyslogd+0x00000058cf50)
>     #2 wtpAdviseMaxWorkers /home/rger/proj/rsyslog/runtime/wtp.c:520:4
> (rsyslogd+0x00000058c783)
>     #3 qqueueAdviseMaxWorkers
> /home/rger/proj/rsyslog/runtime/queue.c:380:3
> (rsyslogd+0x00000059f899)
>     #4 qqueueStart /home/rger/proj/rsyslog/runtime/queue.c:2437:2
> (rsyslogd+0x0000005990bf)
>     #5 StartDA /home/rger/proj/rsyslog/runtime/queue.c:450:9
> (rsyslogd+0x0000005ae6cf)
>     #6 InitDA /home/rger/proj/rsyslog/runtime/queue.c:514:3
> (rsyslogd+0x00000059f281)
>     #7 qqueueStart /home/rger/proj/rsyslog/runtime/queue.c:2430:3
> (rsyslogd+0x00000059905d)
>     #8 startMainQueue /home/rger/proj/rsyslog/tools/rsyslogd.c:829:2
> (rsyslogd+0x0000004afa7f)
>     #9 activateMainQueue
> /home/rger/proj/rsyslog/runtime/rsconf.c:817:10
> (rsyslogd+0x000000524349)
>     #10 activate /home/rger/proj/rsyslog/runtime/rsconf.c:883:2
> (rsyslogd+0x00000051fbf8)
>     #11 initAll /home/rger/proj/rsyslog/tools/rsyslogd.c:1507:2
> (rsyslogd+0x0000004b2b2c)
>     #12 main /home/rger/proj/rsyslog/tools/rsyslogd.c:1957:2
> (rsyslogd+0x0000004b151e)
>
> SUMMARY: ThreadSanitizer: data race
> (/home/rger/proj/rsyslog/tools/rsyslogd+0x43a830) in
> __interceptor_pthread_setcancelstate


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