linux-kernel - Re: dcache shrink list corruption?

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Message-ID: <20140502210813.GB32527@tucsk.piliscsaba.szeredi.hu>
Date:	Fri, 2 May 2014 23:08:13 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: dcache shrink list corruption?

There's more of the "delete from shrink list not owned by us" in select parent.
Proposed patch appended.

And I'm not sure what umount_collect() is supposed to do.  Can other shrinkers
still be active at that point?  That would present other problems, no?

Also somewhat related is the question: how check_submounts_and_drop() could be
guaranteed correctness (timely removal of all unsed dentries) in the presence of
other shrinkers?

Thanks,
Miklos
----


From: Miklos Szeredi <mszeredi@...e.cz>
Subject: dcache: select_collect(): don't remove from shrink list

Shrink lists are not protected by any lock, so don't remove from an unknown
one.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
---
 fs/dcache.c |   23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1241,18 +1241,19 @@ static enum d_walk_ret select_collect(vo
 	 * loop in shrink_dcache_parent() might not make any progress
 	 * and loop forever.
 	 */
-	if (dentry->d_lockref.count) {
-		dentry_lru_del(dentry);
-	} else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
-		/*
-		 * We can't use d_lru_shrink_move() because we
-		 * need to get the global LRU lock and do the
-		 * LRU accounting.
-		 */
+	if (dentry->d_flags & (DCACHE_SHRINK_LIST | DCACHE_LRU_LIST) ==
+							DCACHE_LRU_LIST) {
 		d_lru_del(dentry);
-		d_shrink_add(dentry, &data->dispose);
-		data->found++;
-		ret = D_WALK_NORETRY;
+		if (!dentry->d_lockref.count) {
+			/*
+			 * We can't use d_lru_shrink_move() because we
+			 * need to get the global LRU lock and do the
+			 * LRU accounting.
+			 */
+			d_shrink_add(dentry, &data->dispose);
+			data->found++;
+			ret = D_WALK_NORETRY;
+		}
 	}
 	/*
 	 * We can return to the caller if we have found some (this
--
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