fuse: block request allocation until io-uring init is complete

Avoid races and block request allocation until io-uring
queues are ready.

This is a especially important for background requests,
as bg request completion might cause lock order inversion
of the typical queue->lock and then fc->bg_lock

    fuse_request_end
       spin_lock(&fc->bg_lock);
       flush_bg_queue
         fuse_send_one
           fuse_uring_queue_fuse_req
           spin_lock(&queue->lock);

Signed-off-by: Bernd Schubert <[email protected]>
Reviewed-by: Luis Henriques <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>

Author: bsbernd

fs/fuse/dev.c

@@ -76,7 +76,8 @@ void fuse_set_initialized(struct fuse_conn *fc)
 
 static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
 {
-	return !fc->initialized || (for_background && fc->blocked);
+	return !fc->initialized || (for_background && fc->blocked) ||
+	       (fc->io_uring && !fuse_uring_ready(fc));
 }
 
 static void fuse_drop_waiting(struct fuse_conn *fc)

fs/fuse/dev_uring.c

@@ -957,6 +957,7 @@ static void fuse_uring_do_register(struct fuse_ring_ent *ent,
 		if (ready) {
 			WRITE_ONCE(fiq->ops, &fuse_io_uring_ops);
 			WRITE_ONCE(ring->ready, true);
+			wake_up_all(&fc->blocked_waitq);
 		}
 	}
 }
@@ -1130,6 +1131,8 @@ int __maybe_unused fuse_uring_cmd(struct io_uring_cmd *cmd,
 		if (err) {
 			pr_info_once("FUSE_IO_URING_CMD_REGISTER failed err=%d\n",
 				     err);
+			fc->io_uring = 0;
+			wake_up_all(&fc->blocked_waitq);
 			return err;
 		}
 		break;

fs/fuse/fuse_i.h

@@ -867,6 +867,9 @@ struct fuse_conn {
 	/* Use pages instead of pointer for kernel I/O */
 	unsigned int use_pages_for_kvec_io:1;
 
+	/* Use io_uring for communication */
+	unsigned int io_uring;
+
 	/** Maximum stack depth for passthrough backing files */
 	int max_stack_depth;
 

fs/fuse/inode.c

@@ -1390,6 +1390,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 				else
 					ok = false;
 			}
+			if (flags & FUSE_OVER_IO_URING && fuse_uring_enabled())
+				fc->io_uring = 1;
 		} else {
 			ra_pages = fc->max_read / PAGE_SIZE;
 			fc->no_lock = 1;