mutex: Fix robust mutex lock acquire (Bug 21778)

65810f0ef05e8c9e333f17a44e77808b163ca298 fixed a robust mutex bug but
introduced BZ 21778: if the CAS used to try to acquire a lock fails, the
expected value is not updated, which breaks other cases in the loce
acquisition loop.  The fix is to simply update the expected value with
the value returned by the CAS, which ensures that behavior is as if the
first case with the CAS never happened (if the CAS fails).

This is a regression introduced in the last release.

Tested on x86_64, i686, ppc64, ppc64le, s390x, aarch64, armv7hl.

diff --git a/ChangeLog b/ChangeLog
index 4cec993f99c9b7aade83f5c49c1435a6a6716ac2..5368e15fb71f16ba59dfdabe2a093bceecff8af6 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,17 @@
-2017-07-23  Nathan Rossi  <nathan@nathanrossi.com>
+2017-07-29  Torvald Riegel  <triegel@redhat.com>
+           Carlos O'Donell  <carlos@redhat.com>
+
+       [BZ 21778]
+       * nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Update
+       oldval if the CAS fails.
+       * nptl/pthread_mutex_lock.c (__pthread_mutex_lock_full): Likewise.
+       * nptl/tst-mutex7.c: Add comments explaining template test.
+       (ROBUST, DELAY_NSEC, ROUNDS, N): New.
+       (tf, do_test): Use them.
+       * nptl/tst-mutex7robust.c: New file.
+       * nptl/Makefile (tests): Add new test.
+
+2017-07-28  Nathan Rossi  <nathan@nathanrossi.com>
 
        [BZ #21779]
        * sysdeps/unix/sysv/linux/microblaze/pt-vfork.S: Branch using PLT.

diff --git a/nptl/Makefile b/nptl/Makefile
index 7e54684a36c2291453bf5d5c3c65c583559b06bd..5cb1bb2c3dfee8394287eb072ccc9f76b68a30d8 100644 (file)
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -230,7 +230,7 @@ LDLIBS-tst-thread_local1 = -lstdc++
 
 tests = tst-attr1 tst-attr2 tst-attr3 tst-default-attr \
        tst-mutex1 tst-mutex2 tst-mutex3 tst-mutex4 tst-mutex5 tst-mutex6 \
-       tst-mutex7 tst-mutex9 tst-mutex5a tst-mutex7a \
+       tst-mutex7 tst-mutex9 tst-mutex5a tst-mutex7a tst-mutex7robust \
        tst-mutexpi1 tst-mutexpi2 tst-mutexpi3 tst-mutexpi4 tst-mutexpi5 \
        tst-mutexpi5a tst-mutexpi6 tst-mutexpi7 tst-mutexpi7a \
        tst-mutexpi9 \

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index b76475bc63acf0d8b618ab2b410137211968ff7a..8c485035eb9b34eff3a38fe529e7fd1c9f6b59b7 100644 (file)
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -197,11 +197,14 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
        {
          /* Try to acquire the lock through a CAS from 0 (not acquired) to
             our TID | assume_other_futex_waiters.  */
-         if (__glibc_likely ((oldval == 0)
-                             && (atomic_compare_and_exchange_bool_acq
-                                 (&mutex->__data.__lock,
-                                  id | assume_other_futex_waiters, 0) == 0)))
-             break;
+         if (__glibc_likely (oldval == 0))
+           {
+             oldval
+               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
+                   id | assume_other_futex_waiters, 0);
+             if (__glibc_likely (oldval == 0))
+               break;
+           }
 
          if ((oldval & FUTEX_OWNER_DIED) != 0)
            {

diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index be5338178ffdefc11db24738e36be50372523abd..d5ec3141f3469e2e7a4cd8a125c87ef4f7658b2a 100644 (file)
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -154,11 +154,14 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
        {
          /* Try to acquire the lock through a CAS from 0 (not acquired) to
             our TID | assume_other_futex_waiters.  */
-         if (__glibc_likely ((oldval == 0)
-                             && (atomic_compare_and_exchange_bool_acq
-                                 (&mutex->__data.__lock,
-                                  id | assume_other_futex_waiters, 0) == 0)))
-             break;
+         if (__glibc_likely (oldval == 0))
+           {
+             oldval
+               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
+                   id | assume_other_futex_waiters, 0);
+             if (__glibc_likely (oldval == 0))
+               break;
+           }
 
          if ((oldval & FUTEX_OWNER_DIED) != 0)
            {

diff --git a/nptl/tst-mutex7.c b/nptl/tst-mutex7.c
index a11afdba5e0ef27ddcb447006f4b623e5765d0e0..08fe251eebba8c7e0ca4b2b95bbe0804f8d69a4a 100644 (file)
--- a/nptl/tst-mutex7.c
+++ b/nptl/tst-mutex7.c
@@ -22,25 +22,41 @@
 #include <stdlib.h>
 #include <time.h>
 
-
+/* This test is a template for other tests to use.  Other tests define
+   the following macros to change the behaviour of the template test.
+   The test is very simple, it configures N threads given the parameters
+   below and then proceeds to go through mutex lock and unlock
+   operations in each thread as described before for the thread
+   function.  */
 #ifndef TYPE
 # define TYPE PTHREAD_MUTEX_DEFAULT
 #endif
-
+#ifndef ROBUST
+# define ROBUST PTHREAD_MUTEX_STALLED
+#endif
+#ifndef DELAY_NSEC
+# define DELAY_NSEC 11000
+#endif
+#ifndef ROUNDS
+# define ROUNDS 1000
+#endif
+#ifndef N
+# define N 100
+#endif
 
 static pthread_mutex_t lock;
 
-
-#define ROUNDS 1000
-#define N 100
-
-
+/* Each thread locks and the subsequently unlocks the lock, yielding
+   the smallest critical section possible.  After the unlock the thread
+   waits DELAY_NSEC nanoseconds before doing the lock and unlock again.
+   Every thread does this ROUNDS times.  The lock and unlock are
+   checked for errors.  */
 static void *
 tf (void *arg)
 {
   int nr = (long int) arg;
   int cnt;
-  struct timespec ts = { .tv_sec = 0, .tv_nsec = 11000 };
+  struct timespec ts = { .tv_sec = 0, .tv_nsec = DELAY_NSEC };
 
   for (cnt = 0; cnt < ROUNDS; ++cnt)
     {
@@ -56,13 +72,16 @@ tf (void *arg)
          return (void *) 1l;
        }
 
-      nanosleep (&ts, NULL);
+      if ((ts.tv_sec > 0) || (ts.tv_nsec > 0))
+       nanosleep (&ts, NULL);
     }
 
   return NULL;
 }
 
-
+/* Setup and run N threads, where each thread does as described
+   in the above thread function.  The threads are given a minimal 1MiB
+   stack since they don't do anything between the lock and unlock.  */
 static int
 do_test (void)
 {
@@ -80,6 +99,12 @@ do_test (void)
       exit (1);
     }
 
+  if (pthread_mutexattr_setrobust (&a, ROBUST) != 0)
+    {
+      puts ("mutexattr_setrobust failed");
+      exit (1);
+    }
+
 #ifdef ENABLE_PI
   if (pthread_mutexattr_setprotocol (&a, PTHREAD_PRIO_INHERIT) != 0)
     {

diff --git a/nptl/tst-mutex7robust.c b/nptl/tst-mutex7robust.c
new file mode 100644 (file)
index 0000000..8221a61
--- /dev/null
+++ b/nptl/tst-mutex7robust.c
@@ -0,0 +1,7 @@
+/* Bug 21778: Fix oversight in robust mutex lock acquisition.  */
+#define TYPE PTHREAD_MUTEX_NORMAL
+#define ROBUST PTHREAD_MUTEX_ROBUST
+#define DELAY_NSEC 0
+#define ROUNDS 1000
+#define N 32
+#include "tst-mutex7.c"