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[PULL,3/5] thread-pool: signal "request_cond" while locked

Message ID 20230801094038.11026-4-anthony.perard@citrix.com (mailing list archive)
State New, archived
Headers show
Series [PULL,1/5] hw/xen: Clarify (lack of) error handling in transaction_commit() | expand

Commit Message

Anthony PERARD Aug. 1, 2023, 9:40 a.m. UTC 
From: Anthony PERARD <anthony.perard@citrix.com>

thread_pool_free() might have been called on the `pool`, which would
be a reason for worker_thread() to quit. In this case,
`pool->request_cond` is been destroyed.

If worker_thread() didn't managed to signal `request_cond` before it
been destroyed by thread_pool_free(), we got:
    util/qemu-thread-posix.c:198: qemu_cond_signal: Assertion `cond->initialized' failed.

One backtrace:
    __GI___assert_fail (assertion=0x55555614abcb "cond->initialized", file=0x55555614ab88 "util/qemu-thread-posix.c", line=198,
	function=0x55555614ad80 <__PRETTY_FUNCTION__.17104> "qemu_cond_signal") at assert.c:101
    qemu_cond_signal (cond=0x7fffb800db30) at util/qemu-thread-posix.c:198
    worker_thread (opaque=0x7fffb800dab0) at util/thread-pool.c:129
    qemu_thread_start (args=0x7fffb8000b20) at util/qemu-thread-posix.c:505
    start_thread (arg=<optimized out>) at pthread_create.c:486

Reported here:
    https://lore.kernel.org/all/ZJwoK50FcnTSfFZ8@MacBook-Air-de-Roger.local/T/#u

To avoid issue, keep lock while sending a signal to `request_cond`.

Fixes: 900fa208f506 ("thread-pool: replace semaphore with condition variable")
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230714152720.5077-1-anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 util/thread-pool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/util/thread-pool.c b/util/thread-pool.c
index 0d97888df0..e3d8292d14 100644
--- a/util/thread-pool.c
+++ b/util/thread-pool.c
@@ -120,13 +120,13 @@  static void *worker_thread(void *opaque)
 
     pool->cur_threads--;
     qemu_cond_signal(&pool->worker_stopped);
-    qemu_mutex_unlock(&pool->lock);
 
     /*
      * Wake up another thread, in case we got a wakeup but decided
      * to exit due to pool->cur_threads > pool->max_threads.
      */
     qemu_cond_signal(&pool->request_cond);
+    qemu_mutex_unlock(&pool->lock);
     return NULL;
 }