lyind commented on a change in pull request #257: GUACAMOLE-958: Avoid
race/deadlock in guacd_timed_client_free()
URL: https://github.com/apache/guacamole-server/pull/257#discussion_r378808997
##########
File path: src/guacd/proc.c
##########
@@ -267,24 +267,24 @@ static int guacd_timed_client_free(guac_client* client,
int timeout) {
.tv_nsec = current_time.tv_usec * 1000
};
- /* Free the client in a separate thread, so we can time the free operation
*/
- if (pthread_create(&client_free_thread, NULL,
- guacd_client_free_thread, &free_operation))
- return 1;
-
/* The mutex associated with the pthread conditional and flag MUST be
* acquired before attempting to wait for the condition */
if (pthread_mutex_lock(&free_operation.completed_mutex))
return 1;
- /* Wait a finite amount of time for the free operation to finish */
- if (pthread_cond_timedwait(&free_operation.completed_cond,
- &free_operation.completed_mutex, &deadline))
- return 1;
+ /* Free the client in a separate thread, so we can time the free operation
*/
+ if (!pthread_create(&client_free_thread, NULL,
+ guacd_client_free_thread, &free_operation)) {
+
+ /* Wait a finite amount of time for the free operation to finish */
+ (void) pthread_cond_timedwait(&free_operation.completed_cond,
Review comment:
<del>
Looking at the code again I believe we should put the
`free_operation->completed = 1;` above the mutex lock in
`guacd_client_free_thread()` to make sure our load/store barrier works.
In the unlikely case where the free-thread sets completed to 1 after a
timeout, we don't care about a possible race-condition (returning a late
success is better than returning a timeout).
</del>
Reading this:
https://stackoverflow.com/questions/3208060/does-guarding-a-variable-with-a-pthread-mutex-guarantee-its-also-not-cached
The initial commit was fine. I will revert the second one and force-push.
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