ovl: skip stale entries in merge dir cache iteration

On the first getdents call, ovl_iterate() populates the readdir cache
with a list of entries, but for upper entries with origin lower inode,
p->ino remains zero.

Following getdents calls traverse the readdir cache list and call
ovl_cache_update_ino() for entries with zero p->ino to lookup the entry
in the overlay and return d_ino that is consistent with st_ino.

If the upper file was unlinked between the first getdents call and the
getdents call that lists the file entry, ovl_cache_update_ino() will not
find the entry and fall back to setting d_ino to the upper real st_ino,
which is inconsistent with how this object was presented to users.

Instead of listing a stale entry with inconsistent d_ino, simply skip
the stale entry, which is better for users.

xfstest overlay/077 is failing without this patch.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/fstests/CAOQ4uxgR_cLnC_vdU5=seP3fwqVkuZM_-WfD6maFTMbMYq=a9w@mail.gmail.com/
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index e8ad2c2c77dd72ef16c237e4901cd1498ca02060..150fdf3bc68d4c812fe45a886c724e58c56f84aa 100644 (file)
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -481,6 +481,8 @@ static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
        }
        this = lookup_one_len(p->name, dir, p->len);
        if (IS_ERR_OR_NULL(this) || !this->d_inode) {
+               /* Mark a stale entry */
+               p->is_whiteout = true;
                if (IS_ERR(this)) {
                        err = PTR_ERR(this);
                        this = NULL;
@@ -776,6 +778,9 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
                                if (err)
                                        goto out;
                        }
+               }
+               /* ovl_cache_update_ino() sets is_whiteout on stale entry */
+               if (!p->is_whiteout) {
                        if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
                                break;
                }