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GNU C Library master sources branch release/2.28/master updated. glibc-2.28-60-g4d7af78
- From: carlos at sourceware dot org
- To: glibc-cvs at sourceware dot org
- Date: 13 Dec 2018 17:29:57 -0000
- Subject: GNU C Library master sources branch release/2.28/master updated. glibc-2.28-60-g4d7af78
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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=4d7af7815af5217db6e8fde6032ddf4f6b2a4420
commit 4d7af7815af5217db6e8fde6032ddf4f6b2a4420
Author: Andreas Schwab <schwab@suse.de>
Date: Thu Nov 8 14:28:22 2018 +0100
Fix rwlock stall with PREFER_WRITER_NONRECURSIVE_NP (bug 23861)
In the read lock function (__pthread_rwlock_rdlock_full) there was a
code path which would fail to reload __readers while waiting for
PTHREAD_RWLOCK_RWAITING to change. This failure to reload __readers
into a local value meant that various conditionals used the old value
of __readers and with only two threads left it could result in an
indefinite stall of one of the readers (waiting for PTHREAD_RWLOCK_RWAITING
to go to zero, but it never would).
(cherry picked from commit f21e8f8ca466320fed38bdb71526c574dae98026)
diff --git a/ChangeLog b/ChangeLog
index 6ad1f7a..c12b599 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2018-12-13 Andreas Schwab <schwab@suse.de>
+
+ [BZ #23861]
+ * nptl/pthread_rwlock_common.c: Reindent. Fix typos.
+ (__pthread_rwlock_rdlock_full): Update expected value for
+ __readers while waiting on PTHREAD_RWLOCK_RWAITING.
+ * nptl/tst-rwlock-pwn.c: New file.
+ * nptl/Makefile (tests): Add tst-rwlock-pwn.
+
2018-12-12 Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
[BZ #23614]
diff --git a/nptl/Makefile b/nptl/Makefile
index ee72096..2d2db64 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -318,7 +318,8 @@ tests = tst-attr1 tst-attr2 tst-attr3 tst-default-attr \
tst-minstack-throw \
tst-cnd-basic tst-mtx-trylock tst-cnd-broadcast \
tst-cnd-timedwait tst-thrd-detach tst-mtx-basic tst-thrd-sleep \
- tst-mtx-recursive tst-tss-basic tst-call-once tst-mtx-timedlock
+ tst-mtx-recursive tst-tss-basic tst-call-once tst-mtx-timedlock \
+ tst-rwlock-pwn
tests-internal := tst-rwlock19 tst-rwlock20 \
tst-sem11 tst-sem12 tst-sem13 \
diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
index a290d08..9ce36d1 100644
--- a/nptl/pthread_rwlock_common.c
+++ b/nptl/pthread_rwlock_common.c
@@ -314,8 +314,8 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
harmless because the flag is just about the state of
__readers, and all threads set the flag under the same
conditions. */
- while ((atomic_load_relaxed (&rwlock->__data.__readers)
- & PTHREAD_RWLOCK_RWAITING) != 0)
+ while (((r = atomic_load_relaxed (&rwlock->__data.__readers))
+ & PTHREAD_RWLOCK_RWAITING) != 0)
{
int private = __pthread_rwlock_get_private (rwlock);
int err = futex_abstimed_wait (&rwlock->__data.__readers,
diff --git a/nptl/tst-rwlock-pwn.c b/nptl/tst-rwlock-pwn.c
new file mode 100644
index 0000000..c39dd70
--- /dev/null
+++ b/nptl/tst-rwlock-pwn.c
@@ -0,0 +1,87 @@
+/* Test rwlock with PREFER_WRITER_NONRECURSIVE_NP (bug 23861).
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ 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; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <support/xthread.h>
+
+/* We choose 10 iterations because this happens to be able to trigger the
+ stall on contemporary hardware. */
+#define LOOPS 10
+/* We need 3 threads to trigger bug 23861. One thread as a writer, and
+ two reader threads. The test verifies that the second-to-last reader
+ is able to notify the *last* reader that it should be done waiting.
+ If the second-to-last reader fails to notify the last reader or does
+ so incorrectly then the last reader may stall indefinitely. */
+#define NTHREADS 3
+
+_Atomic int do_exit;
+pthread_rwlockattr_t mylock_attr;
+pthread_rwlock_t mylock;
+
+void *
+run_loop (void *a)
+{
+ while (!do_exit)
+ {
+ if (random () & 1)
+ {
+ xpthread_rwlock_wrlock (&mylock);
+ xpthread_rwlock_unlock (&mylock);
+ }
+ else
+ {
+ xpthread_rwlock_rdlock (&mylock);
+ xpthread_rwlock_unlock (&mylock);
+ }
+ }
+ return NULL;
+}
+
+int
+do_test (void)
+{
+ xpthread_rwlockattr_init (&mylock_attr);
+ xpthread_rwlockattr_setkind_np (&mylock_attr,
+ PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
+ xpthread_rwlock_init (&mylock, &mylock_attr);
+
+ for (int n = 0; n < LOOPS; n++)
+ {
+ pthread_t tids[NTHREADS];
+ do_exit = 0;
+ for (int i = 0; i < NTHREADS; i++)
+ tids[i] = xpthread_create (NULL, run_loop, NULL);
+ /* Let the threads run for some time. */
+ sleep (1);
+ printf ("Exiting...");
+ fflush (stdout);
+ do_exit = 1;
+ for (int i = 0; i < NTHREADS; i++)
+ xpthread_join (tids[i]);
+ printf ("done.\n");
+ }
+ pthread_rwlock_destroy (&mylock);
+ pthread_rwlockattr_destroy (&mylock_attr);
+ return 0;
+}
+
+#define TIMEOUT (DEFAULT_TIMEOUT + 3 * LOOPS)
+#include <support/test-driver.c>
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 9 ++++
nptl/Makefile | 3 +-
nptl/pthread_rwlock_common.c | 4 +-
nptl/tst-rwlock-pwn.c | 87 ++++++++++++++++++++++++++++++++++++++++++
4 files changed, 100 insertions(+), 3 deletions(-)
create mode 100644 nptl/tst-rwlock-pwn.c
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