| Message ID | 20230714152720.5077-1-anthony.perard@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | thread-pool: signal "request_cond" while locked | expand |
On Fri, Jul 14, 2023 at 04:27:20PM +0100, Anthony PERARD wrote: > 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> > --- > > There's maybe an issue in thread_pool_submit_aio() as well with > signalling `request_cond`, but maybe it's much less likely to be an > issue? The caller must not submit work while destroying the pool, so I'm not sure when this problem could occur with thread_pool_submit_aio()? > --- > util/thread-pool.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) This is QEMU 8.1 material. Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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; }