io_uring/io-wq: make io_wq_work flags atomic

The work flags can be set/accessed from different tasks, both the
originator of the request, and the io-wq workers. While modifications
aren't concurrent, it still makes KMSAN unhappy. There's no real
downside to just making the flag reading/manipulation use proper
atomics here.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Jens Axboe

include/linux/io_uring_types.h

@@ -50,7 +50,7 @@ struct io_wq_work_list {
 
 struct io_wq_work {
 	struct io_wq_work_node list;
-	unsigned flags;
+	atomic_t flags;
 	/* place it here instead of io_kiocb as it fills padding and saves 4B */
 	int cancel_seq;
 };

io_uring/io-wq.c

@@ -159,7 +159,7 @@ static inline struct io_wq_acct *io_get_acct(struct io_wq *wq, bool bound)
 static inline struct io_wq_acct *io_work_get_acct(struct io_wq *wq,
 						  struct io_wq_work *work)
 {
-	return io_get_acct(wq, !(work->flags & IO_WQ_WORK_UNBOUND));
+	return io_get_acct(wq, !(atomic_read(&work->flags) & IO_WQ_WORK_UNBOUND));
 }
 
 static inline struct io_wq_acct *io_wq_get_acct(struct io_worker *worker)
@@ -451,7 +451,7 @@ static void __io_worker_idle(struct io_wq *wq, struct io_worker *worker)
 
 static inline unsigned int io_get_work_hash(struct io_wq_work *work)
 {
-	return work->flags >> IO_WQ_HASH_SHIFT;
+	return atomic_read(&work->flags) >> IO_WQ_HASH_SHIFT;
 }
 
 static bool io_wait_on_hash(struct io_wq *wq, unsigned int hash)
@@ -592,8 +592,9 @@ static void io_worker_handle_work(struct io_wq_acct *acct,
 
 			next_hashed = wq_next_work(work);
 
-			if (unlikely(do_kill) && (work->flags & IO_WQ_WORK_UNBOUND))
-				work->flags |= IO_WQ_WORK_CANCEL;
+			if (do_kill &&
+			    (atomic_read(&work->flags) & IO_WQ_WORK_UNBOUND))
+				atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
 			wq->do_work(work);
 			io_assign_current_work(worker, NULL);
 
@@ -891,7 +892,7 @@ static bool io_wq_worker_wake(struct io_worker *worker, void *data)
 static void io_run_cancel(struct io_wq_work *work, struct io_wq *wq)
 {
 	do {
-		work->flags |= IO_WQ_WORK_CANCEL;
+		atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
 		wq->do_work(work);
 		work = wq->free_work(work);
 	} while (work);
@@ -926,7 +927,7 @@ static bool io_wq_work_match_item(struct io_wq_work *work, void *data)
 void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work)
 {
 	struct io_wq_acct *acct = io_work_get_acct(wq, work);
-	unsigned long work_flags = work->flags;
+	unsigned int work_flags = atomic_read(&work->flags);
 	struct io_cb_cancel_data match = {
 		.fn		= io_wq_work_match_item,
 		.data		= work,
@@ -939,7 +940,7 @@ void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work)
 	 * been marked as one that should not get executed, cancel it here.
 	 */
 	if (test_bit(IO_WQ_BIT_EXIT, &wq->state) ||
-	    (work->flags & IO_WQ_WORK_CANCEL)) {
+	    (work_flags & IO_WQ_WORK_CANCEL)) {
 		io_run_cancel(work, wq);
 		return;
 	}
@@ -982,15 +983,15 @@ void io_wq_hash_work(struct io_wq_work *work, void *val)
 	unsigned int bit;
 
 	bit = hash_ptr(val, IO_WQ_HASH_ORDER);
-	work->flags |= (IO_WQ_WORK_HASHED | (bit << IO_WQ_HASH_SHIFT));
+	atomic_or(IO_WQ_WORK_HASHED | (bit << IO_WQ_HASH_SHIFT), &work->flags);
 }
 
 static bool __io_wq_worker_cancel(struct io_worker *worker,
 				  struct io_cb_cancel_data *match,
 				  struct io_wq_work *work)
 {
 	if (work && match->fn(work, match->data)) {
-		work->flags |= IO_WQ_WORK_CANCEL;
+		atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
 		__set_notify_signal(worker->task);
 		return true;
 	}

io_uring/io-wq.h

@@ -56,7 +56,7 @@ bool io_wq_worker_stopped(void);
 
 static inline bool io_wq_is_hashed(struct io_wq_work *work)
 {
-	return work->flags & IO_WQ_WORK_HASHED;
+	return atomic_read(&work->flags) & IO_WQ_WORK_HASHED;
 }
 
 typedef bool (work_cancel_fn)(struct io_wq_work *, void *);

io_uring/io_uring.c

@@ -462,9 +462,9 @@ static void io_prep_async_work(struct io_kiocb *req)
 	}
 
 	req->work.list.next = NULL;
-	req->work.flags = 0;
+	atomic_set(&req->work.flags, 0);
 	if (req->flags & REQ_F_FORCE_ASYNC)
-		req->work.flags |= IO_WQ_WORK_CONCURRENT;
+		atomic_or(IO_WQ_WORK_CONCURRENT, &req->work.flags);
 
 	if (req->file && !(req->flags & REQ_F_FIXED_FILE))
 		req->flags |= io_file_get_flags(req->file);
@@ -480,7 +480,7 @@ static void io_prep_async_work(struct io_kiocb *req)
 			io_wq_hash_work(&req->work, file_inode(req->file));
 	} else if (!req->file || !S_ISBLK(file_inode(req->file)->i_mode)) {
 		if (def->unbound_nonreg_file)
-			req->work.flags |= IO_WQ_WORK_UNBOUND;
+			atomic_or(IO_WQ_WORK_UNBOUND, &req->work.flags);
 	}
 }
 
@@ -520,7 +520,7 @@ static void io_queue_iowq(struct io_kiocb *req)
 	 * worker for it).
 	 */
 	if (WARN_ON_ONCE(!same_thread_group(req->task, current)))
-		req->work.flags |= IO_WQ_WORK_CANCEL;
+		atomic_or(IO_WQ_WORK_CANCEL, &req->work.flags);
 
 	trace_io_uring_queue_async_work(req, io_wq_is_hashed(&req->work));
 	io_wq_enqueue(tctx->io_wq, &req->work);
@@ -1736,14 +1736,14 @@ void io_wq_submit_work(struct io_wq_work *work)
 	io_arm_ltimeout(req);
 
 	/* either cancelled or io-wq is dying, so don't touch tctx->iowq */
-	if (work->flags & IO_WQ_WORK_CANCEL) {
+	if (atomic_read(&work->flags) & IO_WQ_WORK_CANCEL) {
 fail:
 		io_req_task_queue_fail(req, err);
 		return;
 	}
 	if (!io_assign_file(req, def, issue_flags)) {
 		err = -EBADF;
-		work->flags |= IO_WQ_WORK_CANCEL;
+		atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
 		goto fail;
 	}