From faf8c066df0d6bccb54bd74dd696eeb65e1b3bbc Mon Sep 17 00:00:00 2001 From: Carlos O'Donell Date: Fri, 28 Jul 2017 00:22:44 -0400 Subject: rwlock: Fix explicit hand-over (bug 21298) Without this fix, the rwlock can fail to execute the explicit hand-over in certain cases (e.g., empty critical sections that switch quickly between read and write phases). This can then lead to errors in how __wrphase_futex is accessed, which in turn can lead to deadlocks. --- nptl/tst-rwlock20.c | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 116 insertions(+) create mode 100644 nptl/tst-rwlock20.c (limited to 'nptl/tst-rwlock20.c') diff --git a/nptl/tst-rwlock20.c b/nptl/tst-rwlock20.c new file mode 100644 index 0000000000..4aeea2b8f5 --- /dev/null +++ b/nptl/tst-rwlock20.c @@ -0,0 +1,116 @@ +/* Test program for a read-phase / write-phase explicit hand-over. + Copyright (C) 2017 Free Software Foundation, Inc. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; see the file COPYING.LIB. If + not, see . */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* We realy want to set threads to 2 to reproduce this issue. The goal + is to have one primary writer and a single reader, and to hit the + bug that happens in the interleaving of those two phase transitions. + However, on most hardware, adding a second writer seems to help the + interleaving happen slightly more often, say 20% of the time. On a + 16 core ppc64 machine this fails 100% of the time with an unpatched + glibc. On a 8 core x86_64 machine this fails ~93% of the time, but + it doesn't fail at all on a 4 core system, so having available + unloaded cores makes a big difference in reproducibility. On an 8 + core qemu/kvm guest the reproducer reliability drops to ~10%. */ +#define THREADS 3 + +#define KIND PTHREAD_RWLOCK_PREFER_READER_NP + +static pthread_rwlock_t lock; +static int done = 0; + +static void* +tf (void* arg) +{ + while (atomic_load_relaxed (&done) == 0) + { + int rcnt = 0; + int wcnt = 100; + if ((uintptr_t) arg == 0) + { + rcnt = 1; + wcnt = 1; + } + + do + { + if (wcnt) + { + xpthread_rwlock_wrlock (&lock); + xpthread_rwlock_unlock (&lock); + wcnt--; + } + if (rcnt) + { + xpthread_rwlock_rdlock (&lock); + xpthread_rwlock_unlock (&lock); + rcnt--; + } + } + while ((atomic_load_relaxed (&done) == 0) && (rcnt + wcnt > 0)); + + } + return NULL; +} + + + +static int +do_test (void) +{ + pthread_t thr[THREADS]; + int n; + pthread_rwlockattr_t attr; + + xpthread_rwlockattr_init (&attr); + xpthread_rwlockattr_setkind_np (&attr, KIND); + + xpthread_rwlock_init (&lock, &attr); + + /* Make standard error the same as standard output. */ + dup2 (1, 2); + + /* Make sure we see all message, even those on stdout. */ + setvbuf (stdout, NULL, _IONBF, 0); + + for (n = 0; n < THREADS; ++n) + thr[n] = xpthread_create (NULL, tf, (void *) (uintptr_t) n); + + struct timespec delay; + delay.tv_sec = 10; + delay.tv_nsec = 0; + nanosleep (&delay, NULL); + atomic_store_relaxed (&done, 1); + + /* Wait for all the threads. */ + for (n = 0; n < THREADS; ++n) + xpthread_join (thr[n]); + + return 0; +} + +#include -- cgit v1.2.3