path: root/fs/kernfs
diff options
authorLinus Torvalds <>2019-12-06 09:06:58 -0800
committerLinus Torvalds <>2019-12-06 09:06:58 -0800
commit0aecba6173216931c436a03183f4759a4fd4c2f2 (patch)
tree7bfc21b84675a72b28de651df2201d397d9aebe4 /fs/kernfs
parentb0d4beaa5a4b7d31070c41c2e50740304a3f1138 (diff)
parent2fa6b1e01a9b1a54769c394f06cd72c3d12a2d48 (diff)
Merge branch 'fixes' of git://
Pull vfs d_inode/d_flags memory ordering fixes from Al Viro: "Fallout from tree-wide audit for ->d_inode/->d_flags barriers use. Basically, the problem is that negative pinned dentries require careful treatment - unless ->d_lock is locked or parent is held at least shared, another thread can make them positive right under us. Most of the uses turned out to be safe - the main surprises as far as filesystems are concerned were - race in dget_parent() fastpath, that might end up with the caller observing the returned dentry _negative_, due to insufficient barriers. It is positive in memory, but we could end up seeing the wrong value of ->d_inode in CPU cache. Fixed. - manual checks that result of lookup_one_len_unlocked() is positive (and rejection of negatives). Again, insufficient barriers (we might end up with inconsistent observed values of ->d_inode and ->d_flags). Fixed by switching to a new primitive that does the checks itself and returns ERR_PTR(-ENOENT) instead of a negative dentry. That way we get rid of boilerplate converting negatives into ERR_PTR(-ENOENT) in the callers and have a single place to deal with the barrier-related mess - inside fs/namei.c rather than in every caller out there. The guts of pathname resolution *do* need to be careful - the race found by Ritesh is real, as well as several similar races. Fortunately, it turns out that we can take care of that with fairly local changes in there. The tree-wide audit had not been fun, and I hate the idea of repeating it. I think the right approach would be to annotate the places where we are _not_ guaranteed ->d_inode/->d_flags stability and have sparse catch regressions. But I'm still not sure what would be the least invasive way of doing that and it's clearly the next cycle fodder" * 'fixes' of git:// fs/namei.c: fix missing barriers when checking positivity fix dget_parent() fastpath race new helper: lookup_positive_unlocked() fs/namei.c: pull positivity check into follow_managed()
Diffstat (limited to 'fs/kernfs')
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 4d31503abaee..9dc7e7a64e10 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -223,7 +223,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
return ERR_PTR(-EINVAL);
- dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
+ dtmp = lookup_positive_unlocked(kntmp->name, dentry,
if (IS_ERR(dtmp))