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| author | Carlos O'Donell <carlos@redhat.com> | 2019-01-21 22:50:12 -0500 |
|---|---|---|
| committer | Carlos O'Donell <carlos@redhat.com> | 2019-01-31 20:47:55 -0500 |
| commit | 5fc9ed4c4058bfbdf51ad6e7aac7d209b580e8c4 (patch) | |
| tree | 5787bb93e87e93b3191c1d1d8e1bf61f5a99d3c2 /ChangeLog | |
| parent | 932329a5134665bfad601a8709da2602d943fc38 (diff) | |
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nptl: Fix pthread_rwlock_try*lock stalls (Bug 23844)
For a full analysis of both the pthread_rwlock_tryrdlock() stall
and the pthread_rwlock_trywrlock() stall see:
https://sourceware.org/bugzilla/show_bug.cgi?id=23844#c14
In the pthread_rwlock_trydlock() function we fail to inspect for
PTHREAD_RWLOCK_FUTEX_USED in __wrphase_futex and wake the waiting
readers.
In the pthread_rwlock_trywrlock() function we write 1 to
__wrphase_futex and loose the setting of the PTHREAD_RWLOCK_FUTEX_USED
bit, again failing to wake waiting readers during unlock.
The fix in the case of pthread_rwlock_trydlock() is to check for
PTHREAD_RWLOCK_FUTEX_USED and wake the readers.
The fix in the case of pthread_rwlock_trywrlock() is to only write
1 to __wrphase_futex if we installed the write phase, since all other
readers would be spinning waiting for this step.
We add two new tests, one exercises the stall for
pthread_rwlock_trywrlock() which is easy to exercise, and one exercises
the stall for pthread_rwlock_trydlock() which is harder to exercise.
The pthread_rwlock_trywrlock() test fails consistently without the fix,
and passes after. The pthread_rwlock_tryrdlock() test fails roughly
5-10% of the time without the fix, and passes all the time after.
Signed-off-by: Carlos O'Donell <carlos@redhat.com>
Signed-off-by: Torvald Riegel <triegel@redhat.com>
Signed-off-by: Rik Prohaska <prohaska7@gmail.com>
Co-authored-by: Torvald Riegel <triegel@redhat.com>
Co-authored-by: Rik Prohaska <prohaska7@gmail.com>
Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 17 |
1 files changed, 17 insertions, 0 deletions
@@ -1,3 +1,20 @@ +2019-01-31 Carlos O'Donell <carlos@redhat.com> + Torvald Riegel <triegel@redhat.com> + Rik Prohaska <prohaska7@gmail.com> + + [BZ# 23844] + * nptl/Makefile (tests): Add tst-rwlock-tryrdlock-stall, and + tst-rwlock-trywrlock-stall. + * nptl/pthread_rwlock_tryrdlock.c (__pthread_rwlock_tryrdlock): + Wake waiters if PTHREAD_RWLOCK_FUTEX_USED is set. + * nptl/pthread_rwlock_trywrlock.c (__pthread_rwlock_trywrlock): + Set __wrphase_fute to 1 only if we started the write phase. + * nptl/tst-rwlock-tryrdlock-stall.c: New file. + * nptl/tst-rwlock-trywrlock-stall.c: New file. + * support/Makefile (libsupport-routines): Add xpthread_rwlock_destroy. + * support/xpthread_rwlock_destroy.c: New file. + * support/xthread.h: Declare xpthread_rwlock_destroy. + 2019-02-01 Joseph Myers <joseph@codesourcery.com> * scripts/build-many-glibcs.py (Context.checkout): Default MPFR |