[PATCH] iomap: Return zero in case of unsuccessful pagecache invalidation before DIO

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

Filesystems such as btrfs are unable to guarantee page invalidation
because pages could be locked as a part of the extent. Return zero
in case a page cache invalidation is unsuccessful so filesystems can
fallback to buffered I/O. This is similar to
generic_file_direct_write().

This takes care of the following invalidation warning during btrfs
mixed buffered and direct I/O using iomap_dio_rw():

Page cache invalidation failure on direct I/O.  Possible data
corruption due to collision with buffered I/O!

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index e4addfc58107..215315be6233 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -483,9 +483,15 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	 */
 	ret = invalidate_inode_pages2_range(mapping,
 			pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
-	if (ret)
-		dio_warn_stale_pagecache(iocb->ki_filp);
-	ret = 0;
+	/*
+	 * If a page can not be invalidated, return 0 to fall back
+	 * to buffered write.
+	 */
+	if (ret) {
+		if (ret == -EBUSY)
+			ret = 0;
+		goto out_free_dio;
+	}
 
 	if (iov_iter_rw(iter) == WRITE && !wait_for_completion &&
 	    !inode->i_sb->s_dio_done_wq) {

-- 
Goldwyn