[PATCH] cifs: destage dirty pages before re-reading them for cache=none

[Ronnie Sahlberg <lsahlber@redhat.com>]

This is the opposite case of kernel bugzilla 216301.
If we mmap a file using cache=none and then proceed to update the mmapped
area these updates are not reflected in a later pread() of that part of the
file.
To fix this we must first destage any dirty pages in the range before
we allow the pread() to proceed.

Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/file.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 6f38b134a346..1f3eb97ef4ab 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -4271,6 +4271,15 @@ static ssize_t __cifs_readv(
 		len = ctx->len;
 	}
 
+	if (direct) {
+		rc = filemap_write_and_wait_range(file->f_inode->i_mapping,
+						  offset, offset + len - 1);
+		if (rc) {
+			kref_put(&ctx->refcount, cifs_aio_ctx_release);
+			return rc;
+		}
+	}
+
 	/* grab a lock here due to read response handlers can access ctx */
 	mutex_lock(&ctx->aio_mutex);
 
-- 
2.35.3