From c8386296cd1005b6d1128655ae66f00a2f036df9 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Fri, 4 Oct 2019 10:15:37 -0400 Subject: [PATCH] Fix: Disable cancellation around fd tracker lock When using the ust fd tracker LD_PRELOAD library (liblttng-ust-fd.so), cancelling other threads while they issue "close()" leads to deadlocks. Fixes: #1201 Signed-off-by: Mathieu Desnoyers --- liblttng-ust-comm/lttng-ust-fd-tracker.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/liblttng-ust-comm/lttng-ust-fd-tracker.c b/liblttng-ust-comm/lttng-ust-fd-tracker.c index 28289591..1118163a 100644 --- a/liblttng-ust-comm/lttng-ust-fd-tracker.c +++ b/liblttng-ust-comm/lttng-ust-fd-tracker.c @@ -66,6 +66,13 @@ * is also held across fork. */ static pthread_mutex_t ust_safe_guard_fd_mutex = PTHREAD_MUTEX_INITIALIZER; + +/* + * Cancel state when grabbing the ust_safe_guard_fd_mutex. Saved when + * locking, restored on unlock. Protected by ust_safe_guard_fd_mutex. + */ +static int ust_safe_guard_saved_cancelstate; + /* * Track whether we are within lttng-ust or application, for close * system call override by LD_PRELOAD library. @@ -127,6 +134,12 @@ void lttng_ust_init_fd_tracker(void) void lttng_ust_lock_fd_tracker(void) { + int ret, oldstate; + + ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate); + if (ret) { + ERR("pthread_setcancelstate: %s", strerror(ret)); + } URCU_TLS(thread_fd_tracking) = 1; /* * Ensure the compiler don't move the store after the close() @@ -134,10 +147,14 @@ void lttng_ust_lock_fd_tracker(void) */ cmm_barrier(); pthread_mutex_lock(&ust_safe_guard_fd_mutex); + ust_safe_guard_saved_cancelstate = oldstate; } void lttng_ust_unlock_fd_tracker(void) { + int ret, newstate, oldstate; + + newstate = ust_safe_guard_saved_cancelstate; pthread_mutex_unlock(&ust_safe_guard_fd_mutex); /* * Ensure the compiler don't move the store before the close() @@ -145,6 +162,10 @@ void lttng_ust_unlock_fd_tracker(void) */ cmm_barrier(); URCU_TLS(thread_fd_tracking) = 0; + ret = pthread_setcancelstate(newstate, &oldstate); + if (ret) { + ERR("pthread_setcancelstate: %s", strerror(ret)); + } } static int dup_std_fd(int fd) -- 2.34.1