From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail333.us4.mandrillapp.com ([205.201.137.77]:60970 "EHLO mail333.us4.mandrillapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751168AbcCAFiq (ORCPT ); Tue, 1 Mar 2016 00:38:46 -0500 Received: from pmta03.dal05.mailchimp.com (127.0.0.1) by mail333.us4.mandrillapp.com id hqklec174no5 for ; Tue, 1 Mar 2016 05:38:45 +0000 (envelope-from ) From: Subject: Patch "bcache: fix a livelock when we cause a huge number of cache misses" has been added to the 4.4-stable tree To: , , , , , , , Cc: , Message-Id: <145681072333197@kroah.com> Date: Tue, 01 Mar 2016 05:38:45 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled bcache: fix a livelock when we cause a huge number of cache misses to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bcache-fix-a-livelock-when-we-cause-a-huge-number-of-cache-misses.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 2ef9ccbfcb90cf84bdba320a571b18b05c41101b Mon Sep 17 00:00:00 2001 From: Zheng Liu Date: Sun, 29 Nov 2015 17:17:05 -0800 Subject: bcache: fix a livelock when we cause a huge number of cache misses From: Zheng Liu commit 2ef9ccbfcb90cf84bdba320a571b18b05c41101b upstream. Subject : [PATCH v2] bcache: fix a livelock in btree lock Date : Wed, 25 Feb 2015 20:32:09 +0800 (02/25/2015 04:32:09 AM) This commit tries to fix a livelock in bcache. This livelock might happen when we causes a huge number of cache misses simultaneously. When we get a cache miss, bcache will execute the following path. ->cached_dev_make_request() ->cached_dev_read() ->cached_lookup() ->bch->btree_map_keys() ->btree_root() <------------------------ ->bch_btree_map_keys_recurse() | ->cache_lookup_fn() | ->cached_dev_cache_miss() | ->bch_btree_insert_check_key() -| [If btree->seq is not equal to seq + 1, we should return EINTR and traverse btree again.] In bch_btree_insert_check_key() function we first need to check upgrade flag (op->lock == -1), and when this flag is true we need to release read btree->lock and try to take write btree->lock. During taking and releasing this write lock, btree->seq will be monotone increased in order to prevent other threads modify this in cache miss (see btree.h:74). But if there are some cache misses caused by some requested, we could meet a livelock because btree->seq is always changed by others. Thus no one can make progress. This commit will try to take write btree->lock if it encounters a race when we traverse btree. Although it sacrifice the scalability but we can ensure that only one can modify the btree. Signed-off-by: Zheng Liu Tested-by: Joshua Schmid Tested-by: Eric Wheeler Cc: Joshua Schmid Cc: Zhu Yanhai Cc: Kent Overstreet Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- drivers/md/bcache/btree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -2162,8 +2162,10 @@ int bch_btree_insert_check_key(struct bt rw_lock(true, b, b->level); if (b->key.ptr[0] != btree_ptr || - b->seq != seq + 1) + b->seq != seq + 1) { + op->lock = b->level; goto out; + } } SET_KEY_PTRS(check_key, 1); Patches currently in stable-queue which might be from gnehzuil.liu@gmail.com are queue-4.4/bcache-fix-a-livelock-when-we-cause-a-huge-number-of-cache-misses.patch