netfs: Fix setting of BDP_ASYNC from iocb flags

Fix netfs_perform_write() to set BDP_ASYNC if IOCB_NOWAIT is set rather
than if IOCB_SYNC is not set.  It reflects asynchronicity in the sense of
not waiting rather than synchronicity in the sense of not returning until
the op is complete.

Without this, generic/590 fails on cifs in strict caching mode with a
complaint that one of the writes fails with EAGAIN.  The test can be
distilled down to:

        mount -t cifs /my/share /mnt -ostuff
        xfs_io -i -c 'falloc 0 8191M -c fsync -f /mnt/file
        xfs_io -i -c 'pwrite -b 1M -W 0 8191M' /mnt/file

Fixes: c38f4e9 ("netfs: Provide func to copy data to pagecache for buffered write")
Signed-off-by: David Howells <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jens Axboe <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Enzo Matsumiya <[email protected]>
cc: Jens Axboe <[email protected]>
cc: Matthew Wilcox <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: dhowells

fs/netfs/buffered_write.c

@@ -181,7 +181,7 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	struct folio *folio, *writethrough = NULL;
 	enum netfs_how_to_modify howto;
 	enum netfs_folio_trace trace;
-	unsigned int bdp_flags = (iocb->ki_flags & IOCB_SYNC) ? 0: BDP_ASYNC;
+	unsigned int bdp_flags = (iocb->ki_flags & IOCB_NOWAIT) ? BDP_ASYNC : 0;
 	ssize_t written = 0, ret, ret2;
 	loff_t i_size, pos = iocb->ki_pos, from, to;
 	size_t max_chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;