Messages in this thread | | | Subject | Re: [Ocfs2-devel] [PATCH V3] ocfs2: fix dead lock caused by ocfs2_defrag_extent | From | Larry Chen <> | Date | Thu, 1 Nov 2018 20:39:26 +0800 |
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Hi Joseph,
On 11/1/18 7:52 PM, Changwei Ge wrote: > Hello Joseph, > > On 2018/11/1 17:01, Joseph Qi wrote: >> 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 <lchen@suse.com> >>> --- >>> fs/ocfs2/move_extents.c | 47 ++++++++++++++++++++++++++--------------------- >>> 1 file changed, 26 insertions(+), 21 deletions(-) >>> > >> 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. > > I think we can't remove *clusters_to_move* from here as clusters can be reserved latter outsides this function, but we > still have to reserve metadata(extents) in advance. > So we need that argument. >
Yeah, I think clusters_to_move should be reserved, in order to keep the original logic as it was.
But I'm curious about why max_recs_needed should be equal to 2 * extents_to_split + cluster_to_move? Does that mean that each cluster might form an extent??
Thanks, Larry
> Thanks, > Changwei > >> >> 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; >>> >> >> _______________________________________________ >> Ocfs2-devel mailing list >> Ocfs2-devel@oss.oracle.com >> https://oss.oracle.com/mailman/listinfo/ocfs2-devel >> >
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