From: Joseph Qi <jiangqi903@gmail.com>
To: Changwei Ge <ge.changwei@h3c.com>, Larry Chen <lchen@suse.com>,
"mark@fasheh.com" <mark@fasheh.com>,
"jlbec@evilplan.org" <jlbec@evilplan.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [Ocfs2-devel] [PATCH V3] ocfs2: fix dead lock caused by ocfs2_defrag_extent
Date: Thu, 1 Nov 2018 20:15:52 +0800 [thread overview]
Message-ID: <4f96339a-6209-eee1-3792-4720eca35688@gmail.com> (raw)
In-Reply-To: <63ADC13FD55D6546B7DECE290D39E37301277DE397@H3CMLB12-EX.srv.huawei-3com.com>
On 18/11/1 19:52, 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.
>
I was not saying just remove it.
IIUC, clusters_to_move is for reserving data clusters (for meta_ac, we
mostly talk about blocks). Since we have moved data cluster reserve
logic out of ocfs2_lock_allocators_move_extents() now, then left
clusters_to_move related logic here is odd.
>>> 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
>>
next prev parent reply other threads:[~2018-11-01 12:16 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 7:14 [PATCH V3] ocfs2: fix dead lock caused by ocfs2_defrag_extent Larry Chen
2018-11-01 8:58 ` [Ocfs2-devel] " Joseph Qi
2018-11-01 11:52 ` Changwei Ge
2018-11-01 12:15 ` Joseph Qi [this message]
2018-11-01 12:34 ` Changwei Ge
2018-11-02 1:18 ` Joseph Qi
2018-11-01 12:39 ` Larry Chen
2018-11-01 12:48 ` Changwei Ge
2018-11-02 0:53 ` Changwei Ge
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