3.16.37-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream.
Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay. Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.
Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover. Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
- Adjust context
- Also set the flag in __d_materialise_dentry())]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
fs/dcache.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1502,7 +1502,7 @@ struct dentry *d_alloc(struct dentry * p
struct dentry *dentry = __d_alloc(parent->d_sb, name);
if (!dentry)
return NULL;
-
+ dentry->d_flags |= DCACHE_RCUACCESS;
spin_lock(&parent->d_lock);
/*
* don't need child lock because it is not subject
@@ -2354,7 +2354,6 @@ static void __d_rehash(struct dentry * e
{
BUG_ON(!d_unhashed(entry));
hlist_bl_lock(b);
- entry->d_flags |= DCACHE_RCUACCESS;
hlist_bl_add_head_rcu(&entry->d_hash, b);
hlist_bl_unlock(b);
}
@@ -2560,6 +2559,7 @@ static void __d_move(struct dentry *dent
/* ... and switch the parents */
if (IS_ROOT(dentry)) {
+ dentry->d_flags |= DCACHE_RCUACCESS;
dentry->d_parent = target->d_parent;
target->d_parent = target;
INIT_LIST_HEAD(&target->d_child);
@@ -2696,6 +2696,7 @@ static void __d_materialise_dentry(struc
switch_names(dentry, anon, false);
+ dentry->d_flags |= DCACHE_RCUACCESS;
dentry->d_parent = dentry;
list_del_init(&dentry->d_child);
anon->d_parent = dparent;
--
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