[qemu-xen staging] thread-pool: signal "request_cond" while locked

[patchbot@xxxxxxx]

commit 690346043db881debcace7d22249f3355527c5f9
Author:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
AuthorDate: Fri Jul 14 16:27:20 2023 +0100
Commit:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
CommitDate: Tue Aug 1 19:02:38 2023 +0100

    thread-pool: signal "request_cond" while locked
    
    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@xxxxxxxxxx>
    Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
    Message-Id: <20230714152720.5077-1-anthony.perard@xxxxxxxxxx>
    Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    (cherry picked from commit f4f71363fcdb1092ff64d2bba6f9af39570c2f2b)
---
 util/thread-pool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/util/thread-pool.c b/util/thread-pool.c
index 31113b5860..39accc9ebe 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;
 }
 
--
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