link_path_walk(): be careful when failing with ENOTDIR
In RCU mode we might end up with dentry evicted just we check
that it's a directory. In such case we should return ECHILD
rather than ENOTDIR, so that pathwalk would be retries in non-RCU
mode.
Breakage had been introduced in commit b18825a - prior to that
we were looking at nd->inode, which had been fetched before
verifying that ->d_seq was still valid. That form of check
would only be satisfied if at some point the pathname prefix
would indeed have resolved to a non-directory. The fix consists
of checking ->d_seq after we'd run into a non-directory dentry,
and failing with ECHILD in case of mismatch.
Note that all branches since 3.12 have that problem...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index ae4e4c1..fbbcf09 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1954,8 +1954,13 @@
continue;
}
}
- if (unlikely(!d_can_lookup(nd->path.dentry)))
+ if (unlikely(!d_can_lookup(nd->path.dentry))) {
+ if (nd->flags & LOOKUP_RCU) {
+ if (unlazy_walk(nd, NULL, 0))
+ return -ECHILD;
+ }
return -ENOTDIR;
+ }
}
}