linux-kernel - [PATCH 3.2 106/164] d_walk() might skip too much

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Message-ID: <lsq.1438473757.64896801@decadent.org.uk>
Date:	Sun, 02 Aug 2015 01:02:37 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Al Viro" <viro@...iv.linux.org.uk>
Subject: [PATCH 3.2 106/164] d_walk() might skip too much

3.2.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

commit 2159184ea01e4ae7d15f2017e296d4bc82d5aeb0 upstream.

when we find that a child has died while we'd been trying to ascend,
we should go into the first live sibling itself, rather than its sibling.

Off-by-one in question had been introduced in "deal with deadlock in
d_walk()" and the fix needs to be backported to all branches this one
has been backported to.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
[bwh: Backported to 3.2: apply to the 3 copies of this logic we
 ended up with]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/dcache.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1016,13 +1016,13 @@ ascend:
 		/* might go back up the wrong parent if we have had a rename */
 		if (!locked && read_seqretry(&rename_lock, seq))
 			goto rename_retry;
-		next = child->d_child.next;
-		while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) {
+		/* go into the first sibling still alive */
+		do {
+			next = child->d_child.next;
 			if (next == &this_parent->d_subdirs)
 				goto ascend;
 			child = list_entry(next, struct dentry, d_child);
-			next = next->next;
-		}
+		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
 		rcu_read_unlock();
 		goto resume;
 	}
@@ -1142,13 +1142,13 @@ ascend:
 		/* might go back up the wrong parent if we have had a rename */
 		if (!locked && read_seqretry(&rename_lock, seq))
 			goto rename_retry;
-		next = child->d_child.next;
-		while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) {
+		/* go into the first sibling still alive */
+		do {
+			next = child->d_child.next;
 			if (next == &this_parent->d_subdirs)
 				goto ascend;
 			child = list_entry(next, struct dentry, d_child);
-			next = next->next;
-		}
+		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
 		rcu_read_unlock();
 		goto resume;
 	}
@@ -2938,13 +2938,13 @@ ascend:
 		/* might go back up the wrong parent if we have had a rename */
 		if (!locked && read_seqretry(&rename_lock, seq))
 			goto rename_retry;
-		next = child->d_child.next;
-		while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) {
+		/* go into the first sibling still alive */
+		do {
+			next = child->d_child.next;
 			if (next == &this_parent->d_subdirs)
 				goto ascend;
 			child = list_entry(next, struct dentry, d_child);
-			next = next->next;
-		}
+		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
 		rcu_read_unlock();
 		goto resume;
 	}

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