[RFC PATCH] smb: client: force dentry revalidation if nohandlecache is set

[Enzo Matsumiya <ematsumiya@xxxxxxx>]

Some operations return -EEXIST for a non-existing dir/file because of
cached attributes.

Fix this by forcing dentry revalidation when nohandlecache is set.

Bug/reproducer:
Azure Files share, attribute caching timeout is 30s (as
suggested by Azure), 2 clients mounting the same share.

tcon->nohandlecache is set by cifs_get_tcon() because no directory
leasing capability is offered.

    # client 1 and 2
    $ mount.cifs -o ...,actimeo=30 //server/share /mnt
    $ cd /mnt

    # client 1
    $ mkdir dir1

    # client 2
    $ ls
    dir1

    # client 1
    $ mv dir1 dir2

    # client 2
    $ mkdir dir1
    mkdir: cannot create directory ‘dir1’: File exists
    $ ls
    dir2
    $ mkdir dir1
    mkdir: cannot create directory ‘dir1’: File exists

"mkdir dir1" eventually works after 30s (when attribute cache
expired).

The same behaviour can be observed with files if using some
non-overwritting operation (e.g. "rm -i").

Signed-off-by: Enzo Matsumiya <ematsumiya@xxxxxxx>
Tested-by: Henrique Carvalho <henrique.carvalho@xxxxxxxx>
---
 fs/smb/client/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index dd0afa23734c..5f9c5525385f 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -2427,6 +2427,9 @@ cifs_dentry_needs_reval(struct dentry *dentry)
 	if (!lookupCacheEnabled)
 		return true;
 
+	if (tcon->nohandlecache)
+		return true;
+
 	if (!open_cached_dir_by_dentry(tcon, dentry->d_parent, &cfid)) {
 		spin_lock(&cfid->fid_lock);
 		if (cfid->time && cifs_i->time > cfid->time) {
-- 
2.46.0