Use "error-checking" mutexes in place of other kinds wherever possible.

We've seen a number of deadlocks in the tree since thread safety was
introduced.  So far, all of these are self-deadlocks, that is, a single
thread acquiring a lock and then attempting to re-acquire the same lock
recursively.  When this has happened, the process simply hung, and it was
somewhat difficult to find the cause.

POSIX "error-checking" mutexes check for this specific problem (and
others).  This commit switches from other types of mutexes to
error-checking mutexes everywhere that we can, that is, everywhere that
we're not using recursive mutexes.  This ought to help find problems more
quickly in the future.

There might be performance advantages to other kinds of mutexes in some
cases.  However, the existing mutex type choices were just guesses, so I'd
rather go for easy detection of errors until we know that other mutex
types actually perform better in specific cases.  Also, I did a quick
microbenchmark of glibc mutex types on my host and found that the
error checking mutexes weren't any slower than the other types, at least
when the mutex is uncontended.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/lib/ovs-thread.c b/lib/ovs-thread.c
index c1560703..e9366e2d 100644
--- a/lib/ovs-thread.c
+++ b/lib/ovs-thread.c
@@ -132,8 +132,8 @@ typedef void destructor_func(void *);
 XPTHREAD_FUNC2(pthread_key_create, pthread_key_t *, destructor_func *);
 XPTHREAD_FUNC2(pthread_setspecific, pthread_key_t, const void *);
 
-void
-ovs_mutex_init(const struct ovs_mutex *l_, int type)
+static void
+ovs_mutex_init__(const struct ovs_mutex *l_, int type)
 {
     struct ovs_mutex *l = CONST_CAST(struct ovs_mutex *, l_);
     pthread_mutexattr_t attr;
@@ -149,6 +149,20 @@ ovs_mutex_init(const struct ovs_mutex *l_, int type)
     xpthread_mutexattr_destroy(&attr);
 }
 
+/* Initializes 'mutex' as a normal (non-recursive) mutex. */
+void
+ovs_mutex_init(const struct ovs_mutex *mutex)
+{
+    ovs_mutex_init__(mutex, PTHREAD_MUTEX_ERRORCHECK);
+}
+
+/* Initializes 'mutex' as a recursive mutex. */
+void
+ovs_mutex_init_recursive(const struct ovs_mutex *mutex)
+{
+    ovs_mutex_init__(mutex, PTHREAD_MUTEX_RECURSIVE);
+}
+
 void
 ovs_rwlock_init(const struct ovs_rwlock *l_)
 {