[PATCH v7 01/19] smb: client: don't write back through O_DIRECT handles

[Paulo Alcantara <pc@manguebit.org>]

Writeback uses the first writable handle of the inode, which may have
been opened with O_DIRECT.  Such handles are opened with
FILE_NO_INTERMEDIATE_BUFFERING, for which Windows rejects any unaligned
I/O with STATUS_INVALID_PARAMETER.  Writeback of partly dirty pages and
of the unaligned tail of a file through one of them fails, so netfs ends
it with the folios clean and the data never reaches the server.

xfstests generic/051, where fsstress mixes both kinds of opens, loses
about 1% of its writes this way:

  smb3_write_err: ... offset=0xde90d7 len=0xbd0b rc=-22

All the rejected writes in a network capture were unaligned writes on a
no-buffering handle; none of the aligned ones, and none of the unaligned
ones on regular handles, were.

Prefer a handle that was not opened with O_DIRECT, and use one that was
only if there is no other.

Fixes: 1013e760d10e ("SMB3: Don't ignore O_SYNC/O_DSYNC and O_DIRECT flags")
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: stable@vger.kernel.org
---
 fs/smb/client/cifsglob.h |  1 +
 fs/smb/client/file.c     | 15 ++++++++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index d3ca688b6aba..dbf980fcf05b 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1891,6 +1891,7 @@ enum cifs_find_flags {
 	FIND_WITH_DELETE	= (1U << 1),
 	FIND_NO_PENDING_DELETE	= (1U << 2),
 	FIND_OPEN_FLAGS		= (1U << 3),
+	FIND_NO_DIRECT		= (1U << 4),
 };
 
 #define   MID_FREE 0
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 0767eb5f4687..aa2d09dac44c 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -255,9 +255,15 @@ static void cifs_begin_writeback(struct netfs_io_request *wreq)
 	struct cifs_io_request *req = container_of(wreq, struct cifs_io_request, rreq);
 	int ret;
 
-	ret = cifs_get_writable_file(CIFS_I(wreq->inode), FIND_ANY, &req->cfile);
+	ret = cifs_get_writable_file(CIFS_I(wreq->inode), FIND_NO_DIRECT,
+				     &req->cfile);
 	if (ret) {
-		cifs_dbg(VFS, "No writable handle in writepages ret=%d\n", ret);
+		ret = cifs_get_writable_file(CIFS_I(wreq->inode), FIND_ANY,
+					     &req->cfile);
+	}
+	if (ret) {
+		cifs_dbg(VFS, "%s: couldn't find writable handle: %d\n",
+			 __func__, ret);
 		return;
 	}
 
@@ -2722,7 +2728,7 @@ int __cifs_get_writable_file(struct cifsInodeInfo *cifs_inode,
 	}
 
 	if (test_bit(CIFS_INO_TMPFILE, &cifs_inode->flags))
-		find_flags = FIND_ANY;
+		find_flags &= FIND_NO_DIRECT;
 
 	cifs_sb = CIFS_SB(cifs_inode);
 
@@ -2752,6 +2758,9 @@ int __cifs_get_writable_file(struct cifsInodeInfo *cifs_inode,
 		    !open_flags_match(cifs_inode, open_flags,
 				      open_file->f_flags))
 			continue;
+		if ((find_flags & FIND_NO_DIRECT) &&
+		    (open_file->f_flags & O_DIRECT))
+			continue;
 		if (OPEN_FMODE(open_file->f_flags) & FMODE_WRITE) {
 			if (!open_file->invalidHandle) {
 				/* found a good writable file */
-- 
2.56.0