You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
71 lines
2.8 KiB
71 lines
2.8 KiB
commit da767eaaf6128eccd349a54ec6eac2a68dcacacb
|
|
Author: Willy Tarreau <w@1wt.eu>
|
|
Date: Wed Jul 31 19:15:45 2019 +0200
|
|
|
|
BUG/MINOR: debug: fix a small race in the thread dumping code
|
|
|
|
If a thread dump is requested from a signal handler, it may interrupt
|
|
a thread already waiting for a dump to complete, and may see the
|
|
threads_to_dump variable go to zero while others are waiting, steal
|
|
the lock and prevent other threads from ever completing. This tends
|
|
to happen when dumping many threads upon a watchdog timeout, to threads
|
|
waiting for their turn.
|
|
|
|
Instead now we proceed in two steps :
|
|
1) the last dumped thread sets all bits again
|
|
2) all threads only wait for their own bit to appear, then clear it
|
|
and quit
|
|
|
|
This way there's no risk that a bit performs a double flip in the same
|
|
loop and threads cannot get stuck here anymore.
|
|
|
|
This should be backported to 2.0 as it clarifies stack traces.
|
|
|
|
(cherry picked from commit c07736209db764fb2aef6f18ed3687a504c35771)
|
|
Signed-off-by: Willy Tarreau <w@1wt.eu>
|
|
|
|
diff --git a/src/debug.c b/src/debug.c
|
|
index 059bc6b9..07624ca5 100644
|
|
--- a/src/debug.c
|
|
+++ b/src/debug.c
|
|
@@ -440,8 +440,8 @@ void debug_handler(int sig, siginfo_t *si, void *arg)
|
|
* 1- wait for our turn, i.e. when all lower bits are gone.
|
|
* 2- perform the action if our bit is set
|
|
* 3- remove our bit to let the next one go, unless we're
|
|
- * the last one and have to put them all but ours
|
|
- * 4- wait for zero and clear our bit if it's set
|
|
+ * the last one and have to put them all as a signal
|
|
+ * 4- wait out bit to re-appear, then clear it and quit.
|
|
*/
|
|
|
|
/* wait for all previous threads to finish first */
|
|
@@ -454,7 +454,7 @@ void debug_handler(int sig, siginfo_t *si, void *arg)
|
|
ha_thread_dump(thread_dump_buffer, tid, thread_dump_tid);
|
|
if ((threads_to_dump & all_threads_mask) == tid_bit) {
|
|
/* last one */
|
|
- HA_ATOMIC_STORE(&threads_to_dump, all_threads_mask & ~tid_bit);
|
|
+ HA_ATOMIC_STORE(&threads_to_dump, all_threads_mask);
|
|
thread_dump_buffer = NULL;
|
|
}
|
|
else
|
|
@@ -462,14 +462,13 @@ void debug_handler(int sig, siginfo_t *si, void *arg)
|
|
}
|
|
|
|
/* now wait for all others to finish dumping. The last one will set all
|
|
- * bits again to broadcast the leaving condition.
|
|
+ * bits again to broadcast the leaving condition so we'll see ourselves
|
|
+ * present again. This way the threads_to_dump variable never passes to
|
|
+ * zero until all visitors have stopped waiting.
|
|
*/
|
|
- while (threads_to_dump & all_threads_mask) {
|
|
- if (threads_to_dump & tid_bit)
|
|
- HA_ATOMIC_AND(&threads_to_dump, ~tid_bit);
|
|
- else
|
|
- ha_thread_relax();
|
|
- }
|
|
+ while (!(threads_to_dump & tid_bit))
|
|
+ ha_thread_relax();
|
|
+ HA_ATOMIC_AND(&threads_to_dump, ~tid_bit);
|
|
|
|
/* mark the current thread as stuck to detect it upon next invocation
|
|
* if it didn't move.
|