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[3.13.y-ckt,stable] Patch "deal with deadlock in d_walk()" has been added to staging queue

Message ID 1421272394-8302-1-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa Jan. 14, 2015, 9:53 p.m. UTC 
This is a note to let you know that I have just added a patch titled

    deal with deadlock in d_walk()

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

From 7b70ac317cf04e78acf94c506d12b3a775e6b316 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 26 Oct 2014 19:31:10 -0400
Subject: deal with deadlock in d_walk()

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>
[ kamal: backport to 3.13-stable: __dentry_kill() change applied to d_kill() ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 fs/dcache.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

--
1.9.1
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Patch

diff --git a/fs/dcache.c b/fs/dcache.c
index a2ca842..6ef3f68 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -437,7 +437,7 @@  static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
 	__releases(parent->d_lock)
 	__releases(dentry->d_inode->i_lock)
 {
-	list_del(&dentry->d_child);
+	__list_del_entry(&dentry->d_child);
 	/*
 	 * Inform d_walk() that we are no longer attached to the
 	 * dentry tree
@@ -1125,33 +1125,31 @@  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);

@@ -1161,6 +1159,9 @@  out_unlock:
 	return;

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