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Thu, 01 Nov 2018 01:58:53 -0700 (PDT) Subject: Re: [Ocfs2-devel] [PATCH V3] ocfs2: fix dead lock caused by ocfs2_defrag_extent To: Larry Chen , mark@fasheh.com, jlbec@evilplan.org Cc: linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com References: <20181101071422.14470-1-lchen@suse.com> From: Joseph Qi Message-ID: Date: Thu, 1 Nov 2018 16:58:47 +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: <20181101071422.14470-1-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 18/11/1 15:14, Larry Chen wrote: > ocfs2_defrag_extent may fall into deadlock. > > 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 backtrace 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 deadlock 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(). > > ocfs2_lock_allocators_move_extents() is referred 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. > > Change log: > 1. Correct the function comment. > 2. Remove unused argument from ocfs2_lock_meta_allocator_move_extents. > > Signed-off-by: Larry Chen > --- > fs/ocfs2/move_extents.c | 47 ++++++++++++++++++++++++++--------------------- > 1 file changed, 26 insertions(+), 21 deletions(-) > > diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c > index 7eb3b0a6347e..f55f82ca3425 100644 > --- a/fs/ocfs2/move_extents.c > +++ b/fs/ocfs2/move_extents.c > @@ -156,18 +156,14 @@ static int __ocfs2_move_extent(handle_t *handle, > } > > /* > - * lock allocators, and reserving appropriate number of bits for > - * meta blocks and data clusters. > - * > - * in some cases, we don't need to reserve clusters, just let data_ac > - * be NULL. > + * lock allocator, and reserve appropriate number of bits for > + * meta blocks. > */ > -static int ocfs2_lock_allocators_move_extents(struct inode *inode, > +static int ocfs2_lock_meta_allocator_move_extents(struct inode *inode, > struct ocfs2_extent_tree *et, > u32 clusters_to_move, IMO, here clusters_to_move is only for data_ac, since we change this function to only handle meta_ac, I'm afraid clusters_to_move related logic has to been changed correspondingly. Thanks, Joseph > u32 extents_to_split, > struct ocfs2_alloc_context **meta_ac, > - struct ocfs2_alloc_context **data_ac, > int extra_blocks, > int *credits) > { > @@ -192,13 +188,6 @@ 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); > > @@ -257,10 +246,10 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context, > } > } > > - ret = ocfs2_lock_allocators_move_extents(inode, &context->et, *len, 1, > - &context->meta_ac, > - &context->data_ac, > - extra_blocks, &credits); > + ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et, > + *len, 1, > + &context->meta_ac, > + extra_blocks, &credits); > if (ret) { > mlog_errno(ret); > goto out; > @@ -283,6 +272,21 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context, > } > } > > + /* > + * Make sure ocfs2_reserve_cluster is called after > + * __ocfs2_flush_truncate_log, otherwise, dead lock may happen. > + * > + * If ocfs2_reserve_cluster is called > + * before __ocfs2_flush_truncate_log, dead lock on global bitmap > + * may happen. > + * > + */ > + 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); > @@ -600,9 +604,10 @@ static int ocfs2_move_extent(struct ocfs2_move_extents_context *context, > } > } > > - ret = ocfs2_lock_allocators_move_extents(inode, &context->et, len, 1, > - &context->meta_ac, > - NULL, extra_blocks, &credits); > + ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et, > + len, 1, > + &context->meta_ac, > + extra_blocks, &credits); > if (ret) { > mlog_errno(ret); > goto out; >