Message-ID: <87le1sjd2e.fsf@linux.ibm.com>
Date: Tue, 23 Jul 2024 18:19:37 +0200
From: "Marc Hartmayer" <mhartmay@...ux.ibm.com>
To: Lai Jiangshan <jiangshanlai@...il.com>, linux-kernel@...r.kernel.org
Cc: Lai Jiangshan <jiangshan.ljs@...group.com>,
        Valentin Schneider
 <vschneid@...hat.com>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan
 <jiangshanlai@...il.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Sven
 Schnelle <svens@...ux.ibm.com>, Mete Durlu <meted@...ux.ibm.com>
Subject: Re: [PATCH 1/4] workqueue: Reap workers via kthread_stop() and
 remove detach_completion

On Fri, Jun 21, 2024 at 03:32 PM +0800, Lai Jiangshan <jiangshanlai@...il.com> wrote:
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
>
> The code to kick off the destruction of workers is now in a process
> context (idle_cull_fn()), so kthread_stop() can be used in the process
> context to replace the work of pool->detach_completion.
>
> The wakeup in wake_dying_workers() is unneeded after this change, but it
> is harmless, jut keep it here until next patch renames wake_dying_workers()
> rather than renaming it again and again.
>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> ---
>  kernel/workqueue.c | 35 +++++++++++++++++++----------------
>  1 file changed, 19 insertions(+), 16 deletions(-)
>

Hi Lai,

a bisect of a regression in our CI on s390x led to this patch. The bug
is pretty easy to reproduce (currently, I only tested it on s390x - will
try to test it on x86 as well):

1. Start a Linux QEMU/KVM guest with 2 cores using this patch and enable
   `panic_on_warn=1` for the guest kernel.
2. Run the following command in the KVM guest:

  $  dd if=/dev/zero of=/dev/null & while : ; do chcpu -d 1; chcpu -e 1; done

3. Wait for the crash. e.g.:

2024/07/23 18:01:21 [M83LP63]: [  157.267727] ------------[ cut here ]------------
2024/07/23 18:01:21 [M83LP63]: [  157.267735] WARNING: CPU: 21 PID: 725 at kernel/workqueue.c:3340 worker_thread+0x54e/0x558
2024/07/23 18:01:21 [M83LP63]: [  157.267746] Modules linked in: binfmt_misc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables sunrpc dm_service_time s390_trng vfio_ccw mdev vfio_iommu_type1 vfio sch_fq_codel
2024/07/23 18:01:21 [M83LP63]: loop dm_multipath configfs nfnetlink lcs ctcm fsm zfcp scsi_transport_fc ghash_s390 prng chacha_s390 libchacha aes_s390 des_s390 libdes sha3_512_s390 sha3_256_s390 sha512_s390 sha256_s390 sha1_s390 sha_common scm_block eadm_sch scsi_dh_rdac scsi_dh_emc scsi_dh_alua pkey zcrypt rng_core autofs4
2024/07/23 18:01:21 [M83LP63]: [  157.267792] CPU: 21 PID: 725 Comm: kworker/dying Not tainted 6.10.0-rc2-00239-g68f83057b913 #95
2024/07/23 18:01:21 [M83LP63]: [  157.267796] Hardware name: IBM 3906 M04 704 (LPAR)
2024/07/23 18:01:21 [M83LP63]: [  157.267802]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3
2024/07/23 18:01:21 [M83LP63]: [  157.267797] Krnl PSW : 0704d00180000000 000003d600fcd9fa (worker_thread+0x552/0x558)
2024/07/23 18:01:21 [M83LP63]: [  157.267806] Krnl GPRS: 6479696e6700776f 000002c901b62780 000003d602493ec8 000002c914954600
2024/07/23 18:01:21 [M83LP63]: [  157.267809]            0000000000000000 0000000000000008 000002c901a85400 000002c90719e840
2024/07/23 18:01:21 [M83LP63]: [  157.267811]            000002c90719e880 000002c901a85420 000002c91127adf0 000002c901a85400
2024/07/23 18:01:21 [M83LP63]: [  157.267813]            000002c914954600 0000000000000000 000003d600fcd772 000003560452bd98
2024/07/23 18:01:21 [M83LP63]: [  157.267822] Krnl Code: 000003d600fcd9ec: c0e500674262        brasl   %r14,000003d601cb5eb0
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcd9f2: a7f4ffc8            brc     15,000003d600fcd982
2024/07/23 18:01:21 [M83LP63]: [  157.267822]           #000003d600fcd9f6: af000000            mc      0,0
2024/07/23 18:01:21 [M83LP63]: [  157.267822]           >000003d600fcd9fa: a7f4fec2            brc     15,000003d600fcd77e
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcd9fe: 0707                bcr     0,%r7
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcda00: c00400682e10        brcl    0,000003d601cd3620
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcda06: eb7ff0500024        stmg    %r7,%r15,80(%r15)
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcda0c: b90400ef            lgr     %r14,%r15
2024/07/23 18:01:21 [M83LP63]: [  157.267853] Call Trace:
2024/07/23 18:01:21 [M83LP63]: [  157.267855]  [<000003d600fcd9fa>] worker_thread+0x552/0x558
2024/07/23 18:01:21 [M83LP63]: [  157.267859] ([<000003d600fcd772>] worker_thread+0x2ca/0x558)
2024/07/23 18:01:21 [M83LP63]: [  157.267862]  [<000003d600fd6c80>] kthread+0x120/0x128
2024/07/23 18:01:21 [M83LP63]: [  157.267865]  [<000003d600f5305c>] __ret_from_fork+0x3c/0x58
2024/07/23 18:01:21 [M83LP63]: [  157.267868]  [<000003d601cc746a>] ret_from_fork+0xa/0x30
2024/07/23 18:01:21 [M83LP63]: [  157.267873] Last Breaking-Event-Address:
2024/07/23 18:01:21 [M83LP63]: [  157.267874]  [<000003d600fcd778>] worker_thread+0x2d0/0x558
2024/07/23 18:01:21 [M83LP63]: [  157.267879] Kernel panic - not syncing: kernel: panic_on_warn set ...
2024/07/23 18:01:22 [M83LP63]: [  157.267881] CPU: 21 PID: 725 Comm: kworker/dying Not tainted 6.10.0-rc2-00239-g68f83057b913 #95
2024/07/23 18:01:22 [M83LP63]: [  157.267884] Hardware name: IBM 3906 M04 704 (LPAR)
2024/07/23 18:01:22 [M83LP63]: [  157.267885] Call Trace:
2024/07/23 18:01:22 [M83LP63]: [  157.267886]  [<000003d600fa7f8c>] panic+0x1ec/0x308
2024/07/23 18:01:22 [M83LP63]: [  157.267892]  [<000003d600fa822c>] check_panic_on_warn+0x84/0x88
2024/07/23 18:01:22 [M83LP63]: [  157.267896]  [<000003d600fa846e>] __warn+0xa6/0x160
2024/07/23 18:01:22 [M83LP63]: [  157.267899]  [<000003d601c8ac7e>] report_bug+0x146/0x1c0
2024/07/23 18:01:22 [M83LP63]: [  157.267903]  [<000003d600f50e64>] monitor_event_exception+0x44/0x80
2024/07/23 18:01:22 [M83LP63]: [  157.267905]  [<000003d601cb67e0>] __do_pgm_check+0xf0/0x1b0
2024/07/23 18:01:22 [M83LP63]: [  157.267911]  [<000003d601cc75a8>] pgm_check_handler+0x118/0x168
2024/07/23 18:01:22 [M83LP63]: [  157.267914]  [<000003d600fcd9fa>] worker_thread+0x552/0x558
2024/07/23 18:01:22 [M83LP63]: [  157.267917] ([<000003d600fcd772>] worker_thread+0x2ca/0x558)
2024/07/23 18:01:22 [M83LP63]: [  157.267920]  [<000003d600fd6c80>] kthread+0x120/0x128
2024/07/23 18:01:22 [M83LP63]: [  157.267923]  [<000003d600f5305c>] __ret_from_fork+0x3c/0x58
2024/07/23 18:01:22 [M83LP63]: [  157.267926]  [<000003d601cc746a>] ret_from_fork+0xa/0x30

-- 
Kind regards / Beste Grüße
   Marc Hartmayer

IBM Deutschland Research & Development GmbH
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