On Wed, Feb 24, 2016 at 01:21:08PM -0800, Dan Williams wrote:
> On Wed, Dec 30, 2015 at 5:45 AM, Artur Paszkiewicz
> <artur.paszkiewicz@xxxxxxxxx> wrote:
> > Hi,
> >
> > I'm seeing a hang when trying to stop a RAID5 array that is undergoing
> > reshape:
> >
> > [ 99.629924] md: reshape of RAID array md0
> > [ 99.631150] md: minimum _guaranteed_ speed: 1000 KB/sec/disk.
> > [ 99.632737] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for reshape.
> > [ 99.635366] md: using 128k window, over a total of 1047552k.
> > [ 103.819848] md: md0: reshape interrupted.
> > [ 150.127132] INFO: task md0_raid5:3234 blocked for more than 30 seconds.
> > [ 150.128717] Not tainted 4.4.0-rc5+ #54
> > [ 150.129939] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > [ 150.132116] md0_raid5 D ffff88003b1d7ba0 14104 3234 2 0x00000000
> > [ 150.134081] ffff88003b1d7ba0 ffffffff81e104c0 ffff88003bad0000 ffff88003b1d8000
> > [ 150.137205] ffff88003d66380c 0000000000000001 ffff88003d663a50 ffff88003d663800
> > [ 150.139994] ffff88003b1d7bb8 ffffffff81876050 ffff88003d663800 ffff88003b1d7c28
> > [ 150.142606] Call Trace:
> > [ 150.143551] [<ffffffff81876050>] schedule+0x30/0x80
> > [ 150.144883] [<ffffffffa005fc80>] raid5_quiesce+0x200/0x250 [raid456]
> > [ 150.147964] [<ffffffff810882a0>] ? prepare_to_wait_event+0xf0/0xf0
> > [ 150.149661] [<ffffffffa0003bca>] mddev_suspend.part.26+0x7a/0x90 [md_mod]
> > [ 150.151376] [<ffffffffa0003bf7>] mddev_suspend+0x17/0x20 [md_mod]
> > [ 150.153268] [<ffffffffa0064e29>] check_reshape+0xb9/0x6b0 [raid456]
> > [ 150.154869] [<ffffffff8107e63f>] ? set_next_entity+0x9f/0x6d0
> > [ 150.156359] [<ffffffff8107af68>] ? sched_clock_local+0x18/0x80
> > [ 150.157848] [<ffffffff81081400>] ? pick_next_entity+0xa0/0x150
> > [ 150.159348] [<ffffffff810830ae>] ? pick_next_task_fair+0x3fe/0x460
> > [ 150.160887] [<ffffffffa0065471>] raid5_check_reshape+0x51/0xa0 [raid456]
> > [ 150.162482] [<ffffffffa000ba59>] md_check_recovery+0x2f9/0x480 [md_mod]
> > [ 150.164074] [<ffffffffa00697b4>] raid5d+0x34/0x650 [raid456]
> > [ 150.165751] [<ffffffff81876050>] ? schedule+0x30/0x80
> > [ 150.167508] [<ffffffff818786ef>] ? schedule_timeout+0x1ef/0x270
> > [ 150.169784] [<ffffffff81875ac3>] ? __schedule+0x313/0x870
> > [ 150.171194] [<ffffffffa0002e61>] md_thread+0x111/0x130 [md_mod]
> > [ 150.172671] [<ffffffff810882a0>] ? prepare_to_wait_event+0xf0/0xf0
> > [ 150.174206] [<ffffffffa0002d50>] ? find_pers+0x70/0x70 [md_mod]
> > [ 150.175697] [<ffffffff8106c8d4>] kthread+0xc4/0xe0
> > [ 150.178294] [<ffffffff8106c810>] ? kthread_park+0x50/0x50
> > [ 150.179745] [<ffffffff818796df>] ret_from_fork+0x3f/0x70
> > [ 150.181134] [<ffffffff8106c810>] ? kthread_park+0x50/0x50
> >
> > Two tasks end up blocked:
> > 3866 ? D 0:00 [systemd-udevd]
> > 4051 ? D 0:00 [md0_raid5]
> >
> > This happens when udev change event is triggered by mdadm -S and it
> > causes some reads on the array. I think the hang occurs because
> > raid5_quiesce() is called from the raid5d thread and it blocks waiting
> > for active_stripes to become 0, which won't happen, since stripes are
> > released by raid5d. Commit 738a273 ("md/raid5: fix allocation of
> > 'scribble' array.") added mddev_suspend() in resize_chunks(), causing
> > this problem. Skipping mddev_suspend()/mddev_resume() in resize_chunks()
> > when running in raid5d context seems to fix it, but I don't think that's
> > a correct fix...
>
> One approach to spotting the correct fix might be to go add lockdep
> annotations to validate the "locking" order of these events.
>
> See the usage of:
>
> lock_map_acquire(&wq->lockdep_map);
> lock_map_release(&wq->lockdep_map);
>
> ...in the workqueue code as a way to validate flush ordering. For
> example you want lockdep to report when the current thread would
> deadlock due to a circular or ABBA dependency.
Yes, we really add lockdep here.
As for the bug, write requests run in raid5d, mddev_suspend() waits for all IO,
which waits for the write requests. So this is a clear deadlock. I think we
should delete the check_reshape() in md_check_recovery(). If we change
layout/disks/chunk_size, check_reshape() is already called. If we start an
array, the .run() already handles new layout. There is no point
md_check_recovery() check_reshape() again.
Artur, can you check if below works for you?
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 464627b..7fb1103 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8408,8 +8408,7 @@ void md_check_recovery(struct mddev *mddev)
*/
if (mddev->reshape_position != MaxSector) {
- if (mddev->pers->check_reshape == NULL ||
- mddev->pers->check_reshape(mddev) != 0)
+ if (mddev->pers->check_reshape == NULL)
/* Cannot proceed */
goto not_running;
set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
Thanks,
Shaohua
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