[PATCH] CIFS: Fix read after write for files with read caching

[Pavel Shilovsky <piastryyy@gmail.com>]

When we have a READ lease for a file and have just issued a write
operation to the server we need to purge the cache and set oplock/lease
level to NONE to avoid reading stale data. Currently we do that
only if a write operation succedeed thus not covering cases when
a request was sent to the server but a negative error code was
returned later for some other reasons (e.g. -EIOCBQUEUED or -EINTR).
Fix this by turning off caching regardless of the error code being
returned.

The patches fixes generic tests 075 and 112 from the xfs-tests.

Cc: <stable@vger.kernel.org>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
---
 fs/cifs/file.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 9b53f33..4c144c1 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3096,14 +3096,16 @@ cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from)
 	 * these pages but not on the region from pos to ppos+len-1.
 	 */
 	written = cifs_user_writev(iocb, from);
-	if (written > 0 && CIFS_CACHE_READ(cinode)) {
+	if (CIFS_CACHE_READ(cinode)) {
 		/*
-		 * Windows 7 server can delay breaking level2 oplock if a write
-		 * request comes - break it on the client to prevent reading
-		 * an old data.
+		 * We have read level caching and we have just sent a write
+		 * request to the server thus making data in the cache stale.
+		 * Zap the cache and set oplock/lease level to NONE to avoid
+		 * reading stale data from the cache. All subsequent read
+		 * operations will read new data from the server.
 		 */
 		cifs_zap_mapping(inode);
-		cifs_dbg(FYI, "Set no oplock for inode=%p after a write operation\n",
+		cifs_dbg(FYI, "Set Oplock/Lease to NONE for inode=%p after write\n",
 			 inode);
 		cinode->oplock = 0;
 	}
-- 
2.7.4