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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 /support/xthread.h | |
| parent | 932329a5134665bfad601a8709da2602d943fc38 (diff) | |
| download | glibc-5fc9ed4c4058bfbdf51ad6e7aac7d209b580e8c4.tar.gz | |
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 'support/xthread.h')
| -rw-r--r-- | support/xthread.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/support/xthread.h b/support/xthread.h index 47c23235f3..9fe1f68b3b 100644 --- a/support/xthread.h +++ b/support/xthread.h @@ -84,6 +84,7 @@ void xpthread_rwlockattr_setkind_np (pthread_rwlockattr_t *attr, int pref); void xpthread_rwlock_wrlock (pthread_rwlock_t *rwlock); void xpthread_rwlock_rdlock (pthread_rwlock_t *rwlock); void xpthread_rwlock_unlock (pthread_rwlock_t *rwlock); +void xpthread_rwlock_destroy (pthread_rwlock_t *rwlock); __END_DECLS |