From: Martin Wilck <mwilck@xxxxxxxx>
log_safe() could race with log_thread_stop(); simply
checking the value of log_thr has never been safe. By converting the
mutexes to static initializers, we avoid having to destroy them, and thus
possibly accessing a destroyed mutex in log_safe(). Furthermore, taking
both the logev_lock and the logq_lock makes sure the logarea isn't freed
while we are writing to it.
Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
---
libmultipath/log_pthread.c | 39 ++++++++++++++++++++++++--------------
1 file changed, 25 insertions(+), 14 deletions(-)
diff --git a/libmultipath/log_pthread.c b/libmultipath/log_pthread.c
index 3c73941..91c9c19 100644
--- a/libmultipath/log_pthread.c
+++ b/libmultipath/log_pthread.c
@@ -17,31 +17,42 @@
static pthread_t log_thr;
-static pthread_mutex_t logq_lock;
-static pthread_mutex_t logev_lock;
-static pthread_cond_t logev_cond;
+/* logev_lock must not be taken with logq_lock held */
+static pthread_mutex_t logq_lock = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t logev_lock = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t logev_cond = PTHREAD_COND_INITIALIZER;
static int logq_running;
static int log_messages_pending;
void log_safe (int prio, const char * fmt, va_list ap)
{
+ bool running;
+
if (prio > LOG_DEBUG)
prio = LOG_DEBUG;
- if (log_thr == (pthread_t)0) {
- vsyslog(prio, fmt, ap);
- return;
- }
+ /*
+ * logev_lock protects logq_running. By holding it, we avoid a race
+ * with log_thread_stop() -> log_close(), which would free the logarea.
+ */
+ pthread_mutex_lock(&logev_lock);
+ pthread_cleanup_push(cleanup_mutex, &logev_lock);
+ running = logq_running;
- pthread_mutex_lock(&logq_lock);
- log_enqueue(prio, fmt, ap);
- pthread_mutex_unlock(&logq_lock);
+ if (running) {
+ pthread_mutex_lock(&logq_lock);
+ pthread_cleanup_push(cleanup_mutex, &logq_lock);
+ log_enqueue(prio, fmt, ap);
+ pthread_cleanup_pop(1);
- pthread_mutex_lock(&logev_lock);
- log_messages_pending = 1;
- pthread_cond_signal(&logev_cond);
- pthread_mutex_unlock(&logev_lock);
+ log_messages_pending = 1;
+ pthread_cond_signal(&logev_cond);
+ }
+ pthread_cleanup_pop(1);
+
+ if (!running)
+ vsyslog(prio, fmt, ap);
}
static void flush_logqueue (void)
--
2.28.0
--
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