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authorCarlos O'Donell <carlos@systemhalted.org>2017-07-28 00:22:44 -0400
committerCarlos O'Donell <carlos@systemhalted.org>2017-07-28 00:23:58 -0400
commitfaf8c066df0d6bccb54bd74dd696eeb65e1b3bbc (patch)
treeaf22c223947b73a7c22f3add45da6b5c8f204672 /nptl/tst-rwlock20.c
parent2557ae38f3aa599718f34317cd0c150892a92be5 (diff)
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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.
Diffstat (limited to 'nptl/tst-rwlock20.c')
-rw-r--r--nptl/tst-rwlock20.c116
1 files changed, 116 insertions, 0 deletions
diff --git a/nptl/tst-rwlock20.c b/nptl/tst-rwlock20.c
new file mode 100644
index 0000000..4aeea2b
--- /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 <http://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <error.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <time.h>
+#include <atomic.h>
+#include <support/xthread.h>
+
+/* 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 <support/test-driver.c>