[Bug testsuite/79455] c-c++-common/tsan/race_on_mutex.c fails on powerpcle starting with r244854 (where it was activated)

["kelvin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79455

kelvin at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kelvin at gcc dot gnu.org

--- Comment #1 from kelvin at gcc dot gnu.org ---
As of today (svn revision 245252), I'm seeing intermittent success.  This
turned up during routine regression testing of a proposed patch.  Consistently,
the bootstrapped gcc version before my patch was applied succeeds.  Here is an
excerpt from that gcc.log file:

==================                                                              
WARNING: ThreadSanitizer: data race (pid=104133)                                
  Atomic read of size 1 at 0x0000100200d8 by thread T2:                         
    #0 pthread_mutex_lock
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/libs\
anitizer/sanitizer_common/sanitizer_common_interceptors.inc:3607
(libtsan.so.0+\
0x0000000446a4)                                                                 
    #1 Thread2
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/gcc/testsuite/c\
-c++-common/tsan/race_on_mutex.c:22 (race_on_mutex.exe+0x000010000e84)          

  Previous write of size 1 at 0x0000100200d8 by thread T1:                      
    #0 pthread_mutex_init
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/libs\
anitizer/tsan/tsan_interceptors.cc:1117 (libtsan.so.0+0x00000002d1f8)           
    #1 Thread1
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/gcc/testsuite/c\
-c++-common/tsan/race_on_mutex.c:12 (race_on_mutex.exe+0x000010000d54)          

  Location is global 'Mtx' of size 40 at 0x0000100200d8
(race_on_mutex.exe+0x00\
00100200d8)                                                                     

  Thread T2 (tid=104335, running) created by main thread at:                    
    #0 pthread_create
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/libsanit\
izer/tsan/tsan_interceptors.cc:900 (libtsan.so.0+0x00000002c53c)
    #1 main
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/gcc/testsuite/c-c+\
+-common/tsan/race_on_mutex.c:32 (race_on_mutex.exe+0x000010000f70)

  Thread T1 (tid=104334, finished) created by main thread at:
    #0 pthread_create
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/libsanit\
izer/tsan/tsan_interceptors.cc:900 (libtsan.so.0+0x00000002c53c)
    #1 main
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4patch/gcc/testsuite/c-c+\
+-common/tsan/race_on_mutex.c:31 (race_on_mutex.exe+0x000010000f50)

SUMMARY: ThreadSanitizer: data race
/home/kelvin/gcc-root/gcc-trunk4ltc92025.b4\
patch/gcc/testsuite/c-c++-common/tsan/race_on_mutex.c:22 in Thread2
==================
ThreadSanitizer: reported 1 warnings
PASS: c-c++-common/tsan/race_on_mutex.c   -O0  execution test
PASS: c-c++-common/tsan/race_on_mutex.c   -O0  output pattern test, WARNING:
Th\
readSanitizer: data race.*(
|^M
|^M)  Atomic read of size 1 at .* by thread T2:(
|^M
|^M)    #0 pthread_mutex_lock.*    #1 Thread2.* .*(race_on_mutex.c:22|\?{2}:0)
\
(.*)  Previous write of size 1 at .* by thread T1:(
|^M
|^M)    #0 pthread_mutex_init .* (.)*    #1 Thread1.*
.*(race_on_mutex.c:12|\?{\
2}:0) .*

With the gcc.log output for the version of gcc that has my patch, this test is
consistently failing.  The relevant part of the trace output on the version
that fails is quoted below.  Note that the "previous write was of size 8"
instead of size 1, which is what the dg-output directive is looking for.

==================
WARNING: ThreadSanitizer: data race (pid=36311)
  Atomic read of size 1 at 0x0000100200d8 by thread T2:
    #0 pthread_mutex_lock
/home/kelvin/gcc-root/gcc-trunk4ltc92025/libsanitizer\
/sanitizer_common/sanitizer_common_interceptors.inc:3607
(libtsan.so.0+0x000000\
044704)
    #1 Thread2
/home/kelvin/gcc-root/gcc-trunk4ltc92025/gcc/testsuite/c-c++-com\
mon/tsan/race_on_mutex.c:22 (race_on_mutex.exe+0x000010000f24)

  Previous write of size 8 at 0x0000100200d8 by thread T1:
    #0 memset
/home/kelvin/gcc-root/gcc-trunk4ltc92025/libsanitizer/sanitizer_c\
ommon/sanitizer_common_interceptors.inc:558 (libtsan.so.0+0x000000036154)
    #1 pthread_mutex_init <null> (libpthread.so.0+0x00000000b61c)
    #2 Thread1
/home/kelvin/gcc-root/gcc-trunk4ltc92025/gcc/testsuite/c-c++-com\
mon/tsan/race_on_mutex.c:12 (race_on_mutex.exe+0x000010000df4)

  Location is global 'Mtx' of size 40 at 0x0000100200d8
(race_on_mutex.exe+0x00\
00100200d8)

  Thread T2 (tid=36382, running) created by main thread at:
    #0 pthread_create
/home/kelvin/gcc-root/gcc-trunk4ltc92025/libsanitizer/tsa\
n/tsan_interceptors.cc:900 (libtsan.so.0+0x00000002c59c)
    #1 main
/home/kelvin/gcc-root/gcc-trunk4ltc92025/gcc/testsuite/c-c++-common\
/tsan/race_on_mutex.c:32 (race_on_mutex.exe+0x000010001010)

  Thread T1 (tid=36378, finished) created by main thread at:
    #0 pthread_create
/home/kelvin/gcc-root/gcc-trunk4ltc92025/libsanitizer/tsa\
n/tsan_interceptors.cc:900 (libtsan.so.0+0x00000002c59c)
    #1 main
/home/kelvin/gcc-root/gcc-trunk4ltc92025/gcc/testsuite/c-c++-common\
/tsan/race_on_mutex.c:31 (race_on_mutex.exe+0x000010000ff0)

SUMMARY: ThreadSanitizer: data race
/home/kelvin/gcc-root/gcc-trunk4ltc92025/gc\
c/testsuite/c-c++-common/tsan/race_on_mutex.c:22 in Thread2
==================
ThreadSanitizer: reported 1 warnings
PASS: c-c++-common/tsan/race_on_mutex.c   -O0  execution test
FAIL: c-c++-common/tsan/race_on_mutex.c   -O0  output pattern test, is
========\
==========
WARNING: ThreadSanitizer: data race (pid=36311)
  Atomic read of size 1 at 0x0000100200d8 by thread T2:
    #0 pthread_mutex_lock
gcc-trunk4ltc92025/libsanitizer/sanitizer_common/sani\
tizer_common_interceptors.inc:3607 (libtsan.so.0+0x000000044704)
    #1 Thread2 c-c++-common/tsan/race_on_mutex.c:22
(race_on_mutex.exe+0x000010\
000f24)

  Previous write of size 8 at 0x0000100200d8 by thread T1:
    #0 memset
gcc-trunk4ltc92025/libsanitizer/sanitizer_common/sanitizer_common\
_interceptors.inc:558 (libtsan.so.0+0x000000036154)
    #1 pthread_mutex_init <null> (libpthread.so.0+0x00000000b61c)
    #2 Thread1 c-c++-common/tsan/race_on_mutex.c:12
(race_on_mutex.exe+0x000010\
000df4)

  Location is global 'Mtx' of size 40 at 0x0000100200d8
(race_on_mutex.exe+0x00\
00100200d8)

  Thread T2 (tid=36382, running) created by main thread at:
    #0 pthread_create
gcc-trunk4ltc92025/libsanitizer/tsan/tsan_interceptors.cc\
:900 (libtsan.so.0+0x00000002c59c)
    #1 main c-c++-common/tsan/race_on_mutex.c:32
(race_on_mutex.exe+0x000010001\
010)

  Thread T1 (tid=36378, finished) created by main thread at:
    #0 pthread_create
gcc-trunk4ltc92025/libsanitizer/tsan/tsan_interceptors.cc\
:900 (libtsan.so.0+0x00000002c59c)
    #1 main c-c++-common/tsan/race_on_mutex.c:31
(race_on_mutex.exe+0x000010000\
ff0)

SUMMARY: ThreadSanitizer: data race c-c++-common/tsan/race_on_mutex.c:22 in
Thr\
ead2
==================
ThreadSanitizer: reported 1 warnings
, should match WARNING: ThreadSanitizer: data race.*(
|^M
|^M)  Atomic read of size 1 at .* by thread T2:(
|^M
|^M)    #0 pthread_mutex_lock.*    #1 Thread2.* .*(race_on_mutex.c:22|\?{2}:0)
\
(.*)  Previous write of size 1 at .* by thread T1:(
|^M
|^M)    #0 pthread_mutex_init .* (.)*    #1 Thread1.*
.*(race_on_mutex.c:12|\?{\
2}:0) .*


Apparently, the "ThreadSanitizer: data race" warning is only copied to the
testsuite summary file if the test fails.

I don't understand this test well enough to know why the write of size 1 is
converted into a write of size 8, though I'm guessing it might have something
to do with memory alignment and/or cache coherence.  Could it result from
differences between the fast paths and short paths through the library
implementation of the pthread_mutex_lock and unlock services?