diff options
author | Zheng Liu <gnehzuil.liu@gmail.com> | 2015-11-30 04:17:05 +0300 |
---|---|---|
committer | Jens Axboe <axboe@fb.com> | 2015-12-31 06:23:05 +0300 |
commit | 2ef9ccbfcb90cf84bdba320a571b18b05c41101b (patch) | |
tree | 46fb0b846580797b5b27494a594eb17160dfff56 /drivers | |
parent | 39fc8830eb96a559be8554b8df1e0c31f375feaf (diff) | |
download | linux-2ef9ccbfcb90cf84bdba320a571b18b05c41101b.tar.xz |
bcache: fix a livelock when we cause a huge number of cache misses
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 <wenqing.lz@taobao.com>
Tested-by: Joshua Schmid <jschmid@suse.com>
Tested-by: Eric Wheeler <bcache@linux.ewheeler.net>
Cc: Joshua Schmid <jschmid@suse.com>
Cc: Zhu Yanhai <zhu.yanhai@gmail.com>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/md/bcache/btree.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 83392f856dfd..4a1179cbc52e 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -2162,8 +2162,10 @@ int bch_btree_insert_check_key(struct btree *b, struct btree_op *op, 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); |