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    SubjectRe: [Ocfs2-devel] [PATCH V3] ocfs2: fix dead lock caused by ocfs2_defrag_extent
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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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