On 10/09/2017 12:57 PM, NeilBrown wrote:
On Sun, Oct 08 2017, Xiao Ni wrote:
----- Original Message -----
From: "NeilBrown" <neilb@xxxxxxxx>
To: "Xiao Ni" <xni@xxxxxxxxxx>
Cc: linux-raid@xxxxxxxxxxxxxxx
Sent: Friday, October 6, 2017 12:32:19 PM
Subject: Re: [PATCH 0/4] RFC: attempt to remove md deadlocks with metadata without
On Fri, Oct 06 2017, Xiao Ni wrote:
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.
This is OK.
New write bios will not get past md_handle_request().
A write bios that did get past md_handle_request() is still allowed
through md_write_start(). The mddev_suspend() call won't complete until
that write bio has finished.
Hi Neil
Thanks for the explanation. I took some time to read the emails about the
patch cc27b0c78 which introduced this. It's similar with this problem I
countered. But there is a call of function mddev_suspend in level_store.
So add the check of mddev->suspended in md_write_start can fix the problem
"reshape raid5 -> raid6 atop bcache deadlocks at start on md_attr_store /
raid5_make_request".
In function suspend_lo_store it doesn't call mddev_suspend under mddev->reconfig_mutex.
It would if you had applied
[PATCH 3/4] md: use mddev_suspend/resume instead of ->quiesce()
Did you apply all 4 patches?
Sorry, it's my mistake. I insmod the wrong module. I'll apply the four
patches
and do test again.
Thanks. I looks suspend_lo_store() is calling raid5_quiesce() directly
as you say - so a patch is missing.
Yes, thanks for pointing about this.
Hmm, I have a question. Why can't call md_check_recovery when
MD_SB_CHANGE_PENDING
is set in raid5d?
When MD_SB_CHANGE_PENDING is not set, there is no need to call
md_check_recovery(). I wouldn't hurt except that it would be a waste of
time.
I'm confused. If we want to call md_check_recovery when MD_SB_CHANGE_PENDING
is set, it should be
Sorry, I described the condition wrongly.
If any bit is set in ->sb_flags (except MD_SB_CHANGE_PENDING), then
we need to call md_check_recovery(). If none of those other bits
are set, there is no need.
Hmm, so it's the first question. Why can't call md_check_recovery when
MD_SB_CHANGE_PENDING
is set. It needs to update the superblock too when MD_SB_CHANGE_PENDING
is set. I can't
understand this part.
Can it be:
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6299,7 +6299,7 @@ static void raid5d(struct md_thread *thread)
break;
handled += batch_size;
- if (mddev->sb_flags & ~(1 << MD_SB_CHANGE_PENDING)) {
+ if (mddev->sb_flags) {
Best Regards
Xiao
NeilBrown
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