[PATCH 3.16.y-ckt 215/216] deal with deadlock in d_walk()

Luis Henriques
2015-01-12T18:31:18Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit ca5358ef75fc69fee5322a38a340f5739d997c10 upstream.

... by not hitting rename_retry for reasons other than rename having
happened. In other words, do _not_ restart when finding that
between unlocking the child and locking the parent the former got
into __dentry_kill(). Skip the killed siblings instead...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Moritz Muehlenhoff <jmm@inutil.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
fs/dcache.c | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index c73c777b7c3f..e2dc0874a1f0 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -466,7 +466,7 @@ static void __dentry_kill(struct dentry *dentry)
}
/* if it was on the hash then remove it */
__d_drop(dentry);
- list_del(&dentry->d_child);
+ __list_del_entry(&dentry->d_child);
/*
* Inform d_walk() that we are no longer attached to the
* dentry tree
@@ -1120,33 +1120,31 @@ resume:
/*
* All done at this level ... ascend and resume the search.
*/
+ rcu_read_lock();
+ascend:
if (this_parent != parent) {
struct dentry *child = this_parent;
this_parent = child->d_parent;

- rcu_read_lock();
spin_unlock(&child->d_lock);
spin_lock(&this_parent->d_lock);

- /*
- * might go back up the wrong parent if we have had a rename
- * or deletion
- */
- if (this_parent != child->d_parent ||
- (child->d_flags & DCACHE_DENTRY_KILLED) ||
- need_seqretry(&rename_lock, seq)) {
- spin_unlock(&this_parent->d_lock);
- rcu_read_unlock();
+ /* might go back up the wrong parent if we have had a rename. */
+ if (need_seqretry(&rename_lock, seq))
goto rename_retry;
+ next = child->d_child.next;
+ while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) {
+ if (next == &this_parent->d_subdirs)
+ goto ascend;
+ child = list_entry(next, struct dentry, d_child);
+ next = next->next;
}
rcu_read_unlock();
- next = child->d_child.next;
goto resume;
}
- if (need_seqretry(&rename_lock, seq)) {
- spin_unlock(&this_parent->d_lock);
+ if (need_seqretry(&rename_lock, seq))
goto rename_retry;
- }
+ rcu_read_unlock();
if (finish)
finish(data);

@@ -1156,6 +1154,9 @@ out_unlock:
return;

rename_retry:
+ spin_unlock(&this_parent->d_lock);
+ rcu_read_unlock();
+ BUG_ON(seq & 1);
if (!retry)
return;
seq = 1;
--
2.1.4