linux-kernel - Re: Possible reproduction of CSD locking issue

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Message-ID: <4609fe56-7d88-8176-a378-0f465670b37d@suse.com>
Date:   Wed, 26 Jan 2022 07:08:22 +0100
From:   Juergen Gross <jgross@...e.com>
To:     minyard@....org, Ingo Molnar <mingo@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: Possible reproduction of CSD locking issue

On 25.01.22 19:27, Corey Minyard wrote:
> We have a customer that had been seeing CSD lock issues on a Centos 7
> kernel (unfortunately).  I couldn't find anything or any kernel changes
> that might fix it, so I was consdering it was the CSD locking issue you
> have been chasing for a while.

Is this on bare metal or in a virtualized environment?

The bug I was hunting occurred when running under Xen, and in the end I
found a scheduling problem in the Xen hypervisor.

> 
> So I backported the debug patches.  And of course, they stopped seeing
> the issue, at least as much, and they had trouble with the extra CPU
> time the debug code took.  But they just reproduced it.  Here are the
> logs:
> 
> Jan 23 23:39:43 worker0 kernel: [285737.522743] csd: Detected non-responsive CSD lock (#1) on CPU#3, waiting 5000000042 ns for CPU#55 flush_tlb_func+0x0/0xb0(0xffff8e0b3e2afbe8).
> Jan 23 23:39:43 worker0 kernel: [285737.522744]  csd: CSD lock (#1) unresponsive.
> Jan 23 23:39:43 worker0 kernel: [285737.522747]  csd: cnt(0000000): 0000->0000 queue
> Jan 23 23:39:43 worker0 kernel: [285737.522748]  csd: cnt(0000001): ffff->0037 idle
> Jan 23 23:39:43 worker0 kernel: [285737.522749]  csd: cnt(63d8dd8): 0003->0037 ipi
> Jan 23 23:39:43 worker0 kernel: [285737.522750]  csd: cnt(63d8dd9): 0003->0037 ping
> Jan 23 23:39:43 worker0 kernel: [285737.522750]  csd: cnt(63d8dda): 0003->ffff pinged
> Jan 23 23:39:43 worker0 kernel: [285737.522751]  csd: cnt(63d8dea): 0035->0037 pinged
> Jan 23 23:39:43 worker0 kernel: [285737.522752]  csd: cnt(63d8deb): ffff->0037 gotipi
> Jan 23 23:39:43 worker0 kernel: [285737.522752]  csd: cnt(63d8dec): ffff->0037 handle
> Jan 23 23:39:43 worker0 kernel: [285737.522753]  csd: cnt(63d8ded): ffff->0037 dequeue (src CPU 0 == empty)
> Jan 23 23:39:43 worker0 kernel: [285737.522754]  csd: cnt(63d8dee): ffff->0037 hdlend (src CPU 0 == early)
> Jan 23 23:39:43 worker0 kernel: [285737.522754]  csd: cnt(63d8e1f): 0003->0037 queue
> Jan 23 23:39:43 worker0 kernel: [285737.522755]  csd: cnt(63d8e20): 0003->0037 ipi
> Jan 23 23:39:43 worker0 kernel: [285737.522756]  csd: cnt(63d8e21): 0003->0037 ping
> Jan 23 23:39:43 worker0 kernel: [285737.522756]  csd: cnt(63d8e22): 0003->0037 queue
> Jan 23 23:39:43 worker0 kernel: [285737.522757]  csd: cnt(63d8e23): 0003->0037 noipi
> Jan 23 23:39:43 worker0 kernel: [285737.522757]  csd: cnt now: 63fe4cd
> Jan 23 23:39:43 worker0 kernel: [285737.522758] Task dump for CPU 55:
> Jan 23 23:39:43 worker0 kernel: [285737.522761] kubelet         R  running task        0 277695      1 0x00080000
> Jan 23 23:39:43 worker0 kernel: [285737.522761] Call Trace:
> Jan 23 23:39:43 worker0 kernel: [285737.522769]  [<ffffffff84376b6a>] ? __schedule+0x46a/0x990
> Jan 23 23:39:43 worker0 kernel: [285737.522774]  [<ffffffff83db6353>] ? context_tracking_user_enter+0x13/0x20
> Jan 23 23:39:43 worker0 kernel: [285737.522776]  [<ffffffff843775b5>] ? schedule_user+0x45/0x50
> Jan 23 23:39:43 worker0 kernel: [285737.522779]  [<ffffffff8437b518>] ? retint_careful+0x16/0x34
> Jan 23 23:39:43 worker0 kernel: [285737.522780] csd: Re-sending CSD lock (#1) IPI from CPU#03 to CPU#55
> Jan 23 23:39:43 worker0 kernel: [285737.522788] CPU: 3 PID: 54671 Comm: runc:[2:INIT] Kdump: loaded Tainted: G           OE  ------------ T 3.10.0-1062.12.1.rt56.1042.mvista.test.14.el7.x86_64 #1
> Jan 23 23:39:43 worker0 kernel: [285737.522789] Hardware name: Dell Inc. PowerEdge R740/0YWR7D, BIOS 2.9.4 11/06/2020
> Jan 23 23:39:43 worker0 kernel: [285737.522789] Call Trace:
> Jan 23 23:39:43 worker0 kernel: [285737.522793]  [<ffffffff843718ba>] dump_stack+0x19/0x1b
> Jan 23 23:39:43 worker0 kernel: [285737.522798]  [<ffffffff83d0bcd8>] __csd_lock_wait+0x1a8/0x2a0
> Jan 23 23:39:43 worker0 kernel: [285737.522800]  [<ffffffff83c6d870>] ? leave_mm+0x120/0x120
> Jan 23 23:39:43 worker0 kernel: [285737.522802]  [<ffffffff83d0bfa4>] smp_call_function_single+0xc4/0x1b0
> Jan 23 23:39:43 worker0 kernel: [285737.522804]  [<ffffffff83c6d870>] ? leave_mm+0x120/0x120
> Jan 23 23:39:43 worker0 kernel: [285737.522809]  [<ffffffff83e2684b>] ? page_counter_uncharge+0x3b/0x70
> Jan 23 23:39:43 worker0 kernel: [285737.522811]  [<ffffffff83d0c614>] smp_call_function_many+0x344/0x380
> Jan 23 23:39:43 worker0 kernel: [285737.522813]  [<ffffffff83c6d870>] ? leave_mm+0x120/0x120
> Jan 23 23:39:43 worker0 kernel: [285737.522816]  [<ffffffff83c6da38>] native_flush_tlb_others+0xb8/0xc0
> Jan 23 23:39:43 worker0 kernel: [285737.522818]  [<ffffffff83c6dc25>] flush_tlb_page+0x65/0xf0
> Jan 23 23:39:43 worker0 kernel: [285737.522821]  [<ffffffff83dfdf98>] ptep_clear_flush+0x68/0xa0
> Jan 23 23:39:43 worker0 kernel: [285737.522825]  [<ffffffff83de6806>] wp_page_copy.isra.83+0x3d6/0x650
> Jan 23 23:39:43 worker0 kernel: [285737.522828]  [<ffffffff83de8cb4>] do_wp_page+0xb4/0x710
> Jan 23 23:39:43 worker0 kernel: [285737.522832]  [<ffffffff83decbb4>] handle_mm_fault+0x884/0x1340
> Jan 23 23:39:43 worker0 kernel: [285737.522835]  [<ffffffff83cd7799>] ? update_cfs_shares+0xa9/0xf0
> Jan 23 23:39:43 worker0 kernel: [285737.522839]  [<ffffffff8437efc3>] __do_page_fault+0x213/0x5a0
> Jan 23 23:39:43 worker0 kernel: [285737.522841]  [<ffffffff8437f385>] do_page_fault+0x35/0x90
> Jan 23 23:39:43 worker0 kernel: [285737.522842]  [<ffffffff8437b728>] page_fault+0x28/0x30
> Jan 23 23:39:43 worker0 kernel: [285737.522845] csd: CSD lock (#1) got unstuck on CPU#03, CPU#55 released the lock.
> 
> Hopefully this is the issue you are chasing and not something else.
> I've been studying them to see what they mean, but I thought you might
> be interested to get them asap.

As said before: I've solved my problem.

But I can share some more insight from my experience:

Don't be so sure that resending the IPI woke up the cpu again. It might
have been the NMI for getting the target cpu's stacktrace which resulted
in letting it run again. I missed this possibility in the beginning and
this was the reason I dismissed the Xen scheduling issue too early.


Juergen

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