Re: [PATCH 0/4] RFC: attempt to remove md deadlocks with metadata without

[Xiao Ni <xni@redhat.com>]

On 10/05/2017 01:17 PM, NeilBrown wrote:
> On Thu, Sep 14 2017, Xiao Ni wrote:
>
>>> What do
>>>   cat /proc/8987/stack
>>>   cat /proc/8983/stack
>>>   cat /proc/8966/stack
>>>   cat /proc/8381/stack
>>>
>>> show??
> ...
>
>> /usr/sbin/mdadm --grow --continue /dev/md0. Is it the reason to add lockdep_assert_held(&mddev->reconfig_mutex)?
>> [root@dell-pr1700-02 ~]# cat /proc/8983/stack
>> [<ffffffffa0a3464c>] mddev_suspend+0x12c/0x160 [md_mod]
>> [<ffffffffa0a379ec>] suspend_lo_store+0x7c/0xe0 [md_mod]
>> [<ffffffffa0a3b7d0>] md_attr_store+0x80/0xc0 [md_mod]
>> [<ffffffff812ec8da>] sysfs_kf_write+0x3a/0x50
>> [<ffffffff812ec39f>] kernfs_fop_write+0xff/0x180
>> [<ffffffff81260457>] __vfs_write+0x37/0x170
>> [<ffffffff812619e2>] vfs_write+0xb2/0x1b0
>> [<ffffffff81263015>] SyS_write+0x55/0xc0
>> [<ffffffff810037c7>] do_syscall_64+0x67/0x150
>> [<ffffffff81777527>] entry_SYSCALL64_slow_path+0x25/0x25
>> [<ffffffffffffffff>] 0xffffffffffffffff
>>
>> [jbd2/md0-8]
>> [root@dell-pr1700-02 ~]# cat /proc/8966/stack
>> [<ffffffffa0a39b20>] md_write_start+0xf0/0x220 [md_mod]
>> [<ffffffffa0972b49>] raid5_make_request+0x89/0x8b0 [raid456]
>> [<ffffffffa0a34175>] md_make_request+0xf5/0x260 [md_mod]
>> [<ffffffff81376427>] generic_make_request+0x117/0x2f0
>> [<ffffffff81376675>] submit_bio+0x75/0x150
>> [<ffffffff8129e0b0>] submit_bh_wbc+0x140/0x170
>> [<ffffffff8129e683>] submit_bh+0x13/0x20
>> [<ffffffffa0957e29>] jbd2_write_superblock+0x109/0x230 [jbd2]
>> [<ffffffffa0957f8b>] jbd2_journal_update_sb_log_tail+0x3b/0x80 [jbd2]
>> [<ffffffffa09517ff>] jbd2_journal_commit_transaction+0x16ef/0x19e0 [jbd2]
>> [<ffffffffa0955d02>] kjournald2+0xd2/0x260 [jbd2]
>> [<ffffffff810c73f9>] kthread+0x109/0x140
>> [<ffffffff817776c5>] ret_from_fork+0x25/0x30
>> [<ffffffffffffffff>] 0xffffffffffffffff
> Thanks for this (and sorry it took so long to get to it).
> It looks like
>
> Commit: cc27b0c78c79 ("md: fix deadlock between mddev_suspend() and md_write_start()")
>
> is badly broken.  I wonder how it ever passed testing.
>
> In write_start() is change the wait_event() call to
>
> 	wait_event(mddev->sb_wait,
> 		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) && !mddev->suspended);
>
>
> That should be
>
> 	wait_event(mddev->sb_wait,
> 		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) || mddev->suspended);
Hi Neil

Do we want write bio can be handled when mddev->suspended is 1? After 
changing to this,
write bio can be handled when mddev->suspended is 1.

When the stuck happens, mddev->suspended is 0 and MD_SB_CHANGE_PENDING 
is set. So
the patch can't fix this problem. I tried the patch, the problem still 
exists.

[ 7710.589274] mddev suspend : 0
[ 7710.592228] mddev ro : 0
[ 7710.594746] mddev insync : 0
[ 7710.597620] mddev SB CHANGE PENDING is set
[ 7710.601698] mddev SB CHANGE CLEAN is set
[ 7710.605601] mddev->persistent : 1
[ 7710.608905] mddev->external : 0
[ 7710.612030] conf quiesce : 2

raid5 is still spinning.

Hmm, I have a question. Why can't call md_check_recovery when 
MD_SB_CHANGE_PENDING
is set in raid5d?

                 if (mddev->sb_flags & ~(1 << MD_SB_CHANGE_PENDING)) {
                         spin_unlock_irq(&conf->device_lock);
                         md_check_recovery(mddev);
                         spin_lock_irq(&conf->device_lock);
                 }

Best Regards
Xiao


>
> i.e. it was (!A && !B), it should be (!A || B) !!!!!
>
> Could you please make that change and try again.
Hi Neil

I tried the patch and it can't work.
>
> Thanks,
> NeilBrown