fix potential deadlock between multithreaded fork and aio

[musl] / src / aio / aio.c

diff --git a/src/aio/aio.c b/src/aio/aio.c
index fa24f6b..82f8ecc 100644 (file)
--- a/src/aio/aio.c
+++ b/src/aio/aio.c
@@ -401,11 +401,26 @@ void __aio_atfork(int who)
        if (who<0) {
                pthread_rwlock_rdlock(&maplock);
                return;
+       } else if (!who) {
+               pthread_rwlock_unlock(&maplock);
+               return;
        }
-       if (who>0 && map) for (int a=0; a<(-1U/2+1)>>24; a++)
+       aio_fd_cnt = 0;
+       if (pthread_rwlock_tryrdlock(&maplock)) {
+               /* Obtaining lock may fail if _Fork was called nor via
+                * fork. In this case, no further aio is possible from
+                * child and we can just null out map so __aio_close
+                * does not attempt to do anything. */
+               map = 0;
+               return;
+       }
+       if (map) for (int a=0; a<(-1U/2+1)>>24; a++)
                if (map[a]) for (int b=0; b<256; b++)
                        if (map[a][b]) for (int c=0; c<256; c++)
                                if (map[a][b][c]) for (int d=0; d<256; d++)
                                        map[a][b][c][d] = 0;
-       pthread_rwlock_unlock(&maplock);
+       /* Re-initialize the rwlock rather than unlocking since there
+        * may have been more than one reference on it in the parent.
+        * We are not a lock holder anyway; the thread in the parent was. */
+       pthread_rwlock_init(&maplock, 0);
 }