io_uring: unlock if __io_run_local_work locked inside

It is possible for tw to lock the ring, and this was not propogated out to
io_run_local_work. This can cause an unlock to be missed.

Instead pass a pointer to locked into __io_run_local_work.

Fixes: 8ac5d85a ("io_uring: add local task_work run helper that is entered locked")
Signed-off-by: Dylan Yudaken <dylany@meta.com>
Link: https://lore.kernel.org/r/20221027144429.3971400-3-dylany@meta.com
[axboe: WARN_ON() -> WARN_ON_ONCE() and add a minor comment]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -1173,7 +1173,7 @@ static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
 	}
 }
 
-int __io_run_local_work(struct io_ring_ctx *ctx, bool locked)
+int __io_run_local_work(struct io_ring_ctx *ctx, bool *locked)
 {
 	struct llist_node *node;
 	struct llist_node fake;
@@ -1192,7 +1192,7 @@ int __io_run_local_work(struct io_ring_ctx *ctx, bool locked)
 		struct io_kiocb *req = container_of(node, struct io_kiocb,
 						    io_task_work.node);
 		prefetch(container_of(next, struct io_kiocb, io_task_work.node));
-		req->io_task_work.func(req, &locked);
+		req->io_task_work.func(req, locked);
 		ret++;
 		node = next;
 	}
@@ -1208,7 +1208,7 @@ int __io_run_local_work(struct io_ring_ctx *ctx, bool locked)
 		goto again;
 	}
 
-	if (locked)
+	if (*locked)
 		io_submit_flush_completions(ctx);
 	trace_io_uring_local_work_run(ctx, ret, loops);
 	return ret;
@@ -1225,7 +1225,7 @@ int io_run_local_work(struct io_ring_ctx *ctx)
 
 	__set_current_state(TASK_RUNNING);
 	locked = mutex_trylock(&ctx->uring_lock);
-	ret = __io_run_local_work(ctx, locked);
+	ret = __io_run_local_work(ctx, &locked);
 	if (locked)
 		mutex_unlock(&ctx->uring_lock);
 

io_uring/io_uring.h

@@ -27,7 +27,7 @@ enum {
 struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx, bool overflow);
 bool io_req_cqe_overflow(struct io_kiocb *req);
 int io_run_task_work_sig(struct io_ring_ctx *ctx);
-int __io_run_local_work(struct io_ring_ctx *ctx, bool locked);
+int __io_run_local_work(struct io_ring_ctx *ctx, bool *locked);
 int io_run_local_work(struct io_ring_ctx *ctx);
 void io_req_complete_failed(struct io_kiocb *req, s32 res);
 void __io_req_complete(struct io_kiocb *req, unsigned issue_flags);
@@ -277,9 +277,18 @@ static inline int io_run_task_work_ctx(struct io_ring_ctx *ctx)
 
 static inline int io_run_local_work_locked(struct io_ring_ctx *ctx)
 {
+	bool locked;
+	int ret;
+
 	if (llist_empty(&ctx->work_llist))
 		return 0;
-	return __io_run_local_work(ctx, true);
+
+	locked = true;
+	ret = __io_run_local_work(ctx, &locked);
+	/* shouldn't happen! */
+	if (WARN_ON_ONCE(!locked))
+		mutex_lock(&ctx->uring_lock);
+	return ret;
 }
 
 static inline void io_tw_lock(struct io_ring_ctx *ctx, bool *locked)