From mboxrd@z Thu Jan 1 00:00:00 1970 From: Coly Li Subject: Re: [PATCH V2] bcache: fix potential deadlock problem in btree_gc_coalesce Date: Sun, 26 Apr 2020 17:36:35 +0800 Message-ID: References: <8a6f5fe3-33f9-48e2-e347-05781c3295fd@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Received: from mx2.suse.de ([195.135.220.15]:58476 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726112AbgDZJgm (ORCPT ); Sun, 26 Apr 2020 05:36:42 -0400 In-Reply-To: <8a6f5fe3-33f9-48e2-e347-05781c3295fd@huawei.com> Content-Language: en-US Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: Zhiqiang Liu , kmo@daterainc.com, linux-bcache@vger.kernel.org, "linux-kernel@vger.kernel.org" Cc: "wubo (T)" , Mingfangsen , Yanxiaodan , linfeilong , renxudong On 2020/4/26 16:06, Zhiqiang Liu wrote: > From: Zhiqiang Liu > > coccicheck reports: > drivers/md//bcache/btree.c:1538:1-7: preceding lock on line 1417 > > btree_gc_coalesce func is designed to coalesce two adjacent nodes in > new_nodes[GC_MERGE_NODES] and finally release one node. All nodes`write_lock, > new_nodes[i]->write_lock, are holded before coalescing adjacent nodes, > and them will be released after coalescing successfully. > > However, if the coalescing process fails, such as no enough space of new_nodes[1] > to fit all of the remaining keys in new_nodes[0] and realloc keylist failed, we > will goto to out_nocoalesce tag directly without releasing new_nodes[i]->write_lock. > Then, a deadlock will occur after calling btree_node_free to free new_nodes[i], > which also try to acquire new_nodes[i]->write_lock. > > Here, we add a new tag 'out_unlock_nocoalesce' before out_nocoalesce tag to release > new_nodes[i]->write_lock when coalescing process fails. > > -- > V1->V2: rewrite commit log (suggested by Coly Li) and rename the patch > > Fixes: 2a285686c1 ("bcache: btree locking rework") > Signed-off-by: Zhiqiang Liu OK, I will add it to my for-test queue. Thanks. Coly Li > --- > drivers/md/bcache/btree.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c > index fa872df4e770..cad8b0b97e33 100644 > --- a/drivers/md/bcache/btree.c > +++ b/drivers/md/bcache/btree.c > @@ -1447,7 +1447,7 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, > if (__set_blocks(n1, n1->keys + n2->keys, > block_bytes(b->c)) > > btree_blocks(new_nodes[i])) > - goto out_nocoalesce; > + goto out_unlock_nocoalesce; > > keys = n2->keys; > /* Take the key of the node we're getting rid of */ > @@ -1476,7 +1476,7 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, > > if (__bch_keylist_realloc(&keylist, > bkey_u64s(&new_nodes[i]->key))) > - goto out_nocoalesce; > + goto out_unlock_nocoalesce; > > bch_btree_node_write(new_nodes[i], &cl); > bch_keylist_add(&keylist, &new_nodes[i]->key); > @@ -1522,6 +1522,10 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, > /* Invalidated our iterator */ > return -EINTR; > > +out_unlock_nocoalesce: > + for (i = 0; i < nodes; i++) > + mutex_unlock(&new_nodes[i]->write_lock); > + > out_nocoalesce: > closure_sync(&cl); >