Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations

[Brian Foster]

On Wed, Mar 29, 2017 at 01:18:34PM +0200, Michal Hocko wrote:
> On Wed 29-03-17 13:14:42, Ilya Dryomov wrote:
> > On Wed, Mar 29, 2017 at 1:05 PM, Brian Foster <bfoster@xxxxxxxxxx> wrote:
> > > On Wed, Mar 29, 2017 at 12:41:26PM +0200, Michal Hocko wrote:
> > >> [CC xfs guys]
> > >>
> > >> On Wed 29-03-17 11:21:44, Ilya Dryomov wrote:
> > >> [...]
> > >> > This is a set of stack traces from http://tracker.ceph.com/issues/19309
> > >> > (linked in the changelog):
> > >> >
> > >> > Workqueue: ceph-msgr con_work [libceph]
> > >> > ffff8810871cb018 0000000000000046 0000000000000000 ffff881085d40000
> > >> > 0000000000012b00 ffff881025cad428 ffff8810871cbfd8 0000000000012b00
> > >> > ffff880102fc1000 ffff881085d40000 ffff8810871cb038 ffff8810871cb148
> > >> > Call Trace:
> > >> > [<ffffffff816dd629>] schedule+0x29/0x70
> > >> > [<ffffffff816e066d>] schedule_timeout+0x1bd/0x200
> > >> > [<ffffffff81093ffc>] ? ttwu_do_wakeup+0x2c/0x120
> > >> > [<ffffffff81094266>] ? ttwu_do_activate.constprop.135+0x66/0x70
> > >> > [<ffffffff816deb5f>] wait_for_completion+0xbf/0x180
> > >> > [<ffffffff81097cd0>] ? try_to_wake_up+0x390/0x390
> > >> > [<ffffffff81086335>] flush_work+0x165/0x250
> > >>
> > >> I suspect this is xlog_cil_push_now -> flush_work(&cil->xc_push_work)
> > >> right? I kind of got lost where this waits on an IO.
> > >>
> > >
> > > Yep. That means a CIL push is already in progress. We wait on that to
> > > complete here. After that, the resulting task queues execution of
> > > xlog_cil_push_work()->xlog_cil_push() on m_cil_workqueue. That task may
> > > submit I/O to the log.
> > >
> > > I don't see any reference to xlog_cil_push() anywhere in the traces here
> > > or in the bug referenced above, however..?
> > 
> > Well, it's prefaced with "Interesting is:"...  Sergey (the original
> > reporter, CCed here) might still have the rest of them.
> 
> JFTR
> http://tracker.ceph.com/attachments/download/2769/full_kern_trace.txt
> [288420.754637] Workqueue: xfs-cil/rbd1 xlog_cil_push_work [xfs]
> [288420.754638]  ffff880130c1fb38 0000000000000046 ffff880130c1fac8 ffff880130d72180
> [288420.754640]  0000000000012b00 ffff880130c1fad8 ffff880130c1ffd8 0000000000012b00
> [288420.754641]  ffff8810297b6480 ffff880130d72180 ffffffffa03b1264 ffff8820263d6800
> [288420.754643] Call Trace:
> [288420.754652]  [<ffffffffa03b1264>] ? xlog_bdstrat+0x34/0x70 [xfs]
> [288420.754653]  [<ffffffff816dd629>] schedule+0x29/0x70
> [288420.754661]  [<ffffffffa03b3b9c>] xlog_state_get_iclog_space+0xdc/0x2e0 [xfs]
> [288420.754669]  [<ffffffffa03b1264>] ? xlog_bdstrat+0x34/0x70 [xfs]
> [288420.754670]  [<ffffffff81097cd0>] ? try_to_wake_up+0x390/0x390
> [288420.754678]  [<ffffffffa03b4090>] xlog_write+0x190/0x730 [xfs]
> [288420.754686]  [<ffffffffa03b5d9e>] xlog_cil_push+0x24e/0x3e0 [xfs]
> [288420.754693]  [<ffffffffa03b5f45>] xlog_cil_push_work+0x15/0x20 [xfs]
> [288420.754695]  [<ffffffff81084c19>] process_one_work+0x159/0x4f0
> [288420.754697]  [<ffffffff81084fdc>] process_scheduled_works+0x2c/0x40
> [288420.754698]  [<ffffffff8108579b>] worker_thread+0x29b/0x530
> [288420.754699]  [<ffffffff81085500>] ? create_worker+0x1d0/0x1d0
> [288420.754701]  [<ffffffff8108b6f9>] kthread+0xc9/0xe0
> [288420.754703]  [<ffffffff8108b630>] ? flush_kthread_worker+0x90/0x90
> [288420.754705]  [<ffffffff816e1b98>] ret_from_fork+0x58/0x90
> [288420.754707]  [<ffffffff8108b630>] ? flush_kthread_worker+0x90/0x90

Ah, thanks. According to above, xfs_cil is waiting on log space to free
up. This means xfs-cil is probably in:

	xlog_state_get_iclog_space()
	  ->xlog_wait(&log->l_flush_wait, &log->l_icloglock);

l_flush_wait is awoken during log I/O completion handling via the
xfs-log workqueue. That guy is here:

[288420.773968] INFO: task kworker/6:3:420227 blocked for more than 300 seconds.
[288420.773986]       Not tainted 3.18.43-40 #1
[288420.773997] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[288420.774017] kworker/6:3     D ffff880103893650     0 420227      2 0x00000000
[288420.774027] Workqueue: xfs-log/rbd1 xfs_log_worker [xfs]
[288420.774028]  ffff88010357fac8 0000000000000046 0000000000000000 ffff880103893240
[288420.774030]  0000000000012b00 ffff880146361128 ffff88010357ffd8 0000000000012b00
[288420.774031]  ffff8810297b7540 ffff880103893240 ffff88010357fae8 ffff88010357fbf8
[288420.774033] Call Trace:
[288420.774035]  [<ffffffff816dd629>] schedule+0x29/0x70
[288420.774036]  [<ffffffff816e066d>] schedule_timeout+0x1bd/0x200
[288420.774038]  [<ffffffff81093ffc>] ? ttwu_do_wakeup+0x2c/0x120
[288420.774040]  [<ffffffff81094266>] ? ttwu_do_activate.constprop.135+0x66/0x70
[288420.774042]  [<ffffffff816deb5f>] wait_for_completion+0xbf/0x180
[288420.774043]  [<ffffffff81097cd0>] ? try_to_wake_up+0x390/0x390
[288420.774044]  [<ffffffff81086335>] flush_work+0x165/0x250
[288420.774046]  [<ffffffff81082940>] ? worker_detach_from_pool+0xd0/0xd0
[288420.774054]  [<ffffffffa03b65b1>] xlog_cil_force_lsn+0x81/0x200 [xfs]
[288420.774056]  [<ffffffff8109f3cc>] ? dequeue_entity+0x17c/0x520
[288420.774063]  [<ffffffffa03b478e>] _xfs_log_force+0x6e/0x280 [xfs]
[288420.774065]  [<ffffffff810a076c>] ? put_prev_entity+0x3c/0x2e0
[288420.774067]  [<ffffffff8109b315>] ? sched_clock_cpu+0x95/0xd0
[288420.774068]  [<ffffffff810145a2>] ? __switch_to+0xf2/0x5f0
[288420.774076]  [<ffffffffa03b49d9>] xfs_log_force+0x39/0xe0 [xfs]
[288420.774083]  [<ffffffffa03b4aa8>] xfs_log_worker+0x28/0x50 [xfs]
[288420.774085]  [<ffffffff81084c19>] process_one_work+0x159/0x4f0
[288420.774086]  [<ffffffff8108561b>] worker_thread+0x11b/0x530
[288420.774088]  [<ffffffff81085500>] ? create_worker+0x1d0/0x1d0
[288420.774089]  [<ffffffff8108b6f9>] kthread+0xc9/0xe0
[288420.774091]  [<ffffffff8108b630>] ? flush_kthread_worker+0x90/0x90
[288420.774093]  [<ffffffff816e1b98>] ret_from_fork+0x58/0x90
[288420.774095]  [<ffffffff8108b630>] ? flush_kthread_worker+0x90/0x90

... which is back waiting on xfs-cil.

Ilya,

Have you looked into this[1] patch by any chance? Note that 7a29ac474
("xfs: give all workqueues rescuer threads") may also be a potential
band aid for this. Or IOW, the lack thereof in v3.18.z may make this
problem more likely.

Brian

[1] http://www.spinics.net/lists/linux-xfs/msg04886.html

> -- 
> Michal Hocko
> SUSE Labs
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