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Mon, 27 Aug 2018 18:02:22 -0700 (PDT) Subject: Re: [Ocfs2-devel] [PATCH] fix dead lock caused by ocfs2_defrag_extent To: Larry Chen , mfasheh@suse.com, jlbec@evilplan.org Cc: linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com References: <20180827080121.31145-1-lchen@suse.com> From: Joseph Qi Message-ID: <804e11ca-39e3-575b-2e25-a00c95cf1311@gmail.com> Date: Tue, 28 Aug 2018 09:02:17 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180827080121.31145-1-lchen@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Larry, On 18/8/27 16:01, Larry Chen wrote: > ocfs2_defrag_extent may fall into dead lock. > > ocfs2_ioctl_move_extents > ocfs2_ioctl_move_extents > ocfs2_move_extents > ocfs2_defrag_extent > ocfs2_lock_allocators_move_extents > > ocfs2_reserve_clusters > inode_lock GLOBAL_BITMAP_SYSTEM_INODE > > __ocfs2_flush_truncate_log > inode_lock GLOBAL_BITMAP_SYSTEM_INODE > > As back trace shows above, ocfs2_reserve_clusters will call inode_lock > against the global bitmap if local allocator has not sufficient cluters. > Once global bitmap could meet the demand, ocfs2_reserve_cluster will > return success with global bitmap locked. > > After ocfs2_reserve_cluster, if truncate log is full, > __ocfs2_flush_truncate_log will definitely fall into dead lock > because it needs to inode_lock global bitmap, which has > already been locked. > > To fix this bug, we could remove from ocfs2_lock_allocators_move_extents > the code which intends to lock global allocator, and put the removed > code after __ocfs2_flush_truncate_log > > The ocfs2_lock_allocators_move_extents has been refered by 2 places, one > is here, the other does not need the data allocator context, which means > this patch does not affect the caller so far. > After this change, data_ac in ocfs2_lock_allocators_move_extents() is no longer used. So I'd prefer we also clean it up. Thanks, Joseph > > > Signed-off-by: Larry Chen > --- > fs/ocfs2/move_extents.c | 13 ++++++------- > 1 file changed, 6 insertions(+), 7 deletions(-) > > diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c > index 7eb3b0a6347e..064dedf40d74 100644 > --- a/fs/ocfs2/move_extents.c > +++ b/fs/ocfs2/move_extents.c > @@ -192,13 +192,6 @@ static int ocfs2_lock_allocators_move_extents(struct inode *inode, > goto out; > } > > - if (data_ac) { > - ret = ocfs2_reserve_clusters(osb, clusters_to_move, data_ac); > - if (ret) { > - mlog_errno(ret); > - goto out; > - } > - } > > *credits += ocfs2_calc_extend_credits(osb->sb, et->et_root_el); > > @@ -283,6 +276,12 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context, > } > } > > + ret = ocfs2_reserve_clusters(osb, *len, &context->data_ac); > + if (ret) { > + mlog_errno(ret); > + goto out_unlock_mutex; > + } > + > handle = ocfs2_start_trans(osb, credits); > if (IS_ERR(handle)) { > ret = PTR_ERR(handle); >