Merge tag 'io_uring-6.12-20241101' of git://git.kernel.dk/linux

Pull io_uring fix from Jens Axboe:

 - Fix not honoring IOCB_NOWAIT for starting buffered writes in terms of
   calling sb_start_write(), leading to a deadlock if someone is
   attempting to freeze the file system with writes in progress, as each
   side will end up waiting for the other to make progress.

* tag 'io_uring-6.12-20241101' of git://git.kernel.dk/linux:
  io_uring/rw: fix missing NOWAIT check for O_DIRECT start write

Author: torvalds

io_uring/rw.c

@@ -1014,6 +1014,25 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
 	return IOU_OK;
 }
 
+static bool io_kiocb_start_write(struct io_kiocb *req, struct kiocb *kiocb)
+{
+	struct inode *inode;
+	bool ret;
+
+	if (!(req->flags & REQ_F_ISREG))
+		return true;
+	if (!(kiocb->ki_flags & IOCB_NOWAIT)) {
+		kiocb_start_write(kiocb);
+		return true;
+	}
+
+	inode = file_inode(kiocb->ki_filp);
+	ret = sb_start_write_trylock(inode->i_sb);
+	if (ret)
+		__sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);
+	return ret;
+}
+
 int io_write(struct io_kiocb *req, unsigned int issue_flags)
 {
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
@@ -1051,8 +1070,8 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	if (unlikely(ret))
 		return ret;
 
-	if (req->flags & REQ_F_ISREG)
-		kiocb_start_write(kiocb);
+	if (unlikely(!io_kiocb_start_write(req, kiocb)))
+		return -EAGAIN;
 	kiocb->ki_flags |= IOCB_WRITE;
 
 	if (likely(req->file->f_op->write_iter))