Re: workqueue lockup debug
From: John Garry
Date: Tue Oct 29 2024 - 04:08:32 EST
On 29/10/2024 04:11, Dave Chinner wrote:
Can you advise on a robust method to get some debug from this system?
Maybe this is a scheduler issue, as Dave mentioned in that same thread.
I just got a new hit on the scheduler issue on 6.12-rc5:
[ 172.477662] ------------[ cut here ]------------
[ 172.480660] se->on_rq
[ 172.480682] WARNING: CPU: 3 PID: 728318 at kernel/sched/fair.c:5629 pick_task_fair+0xb6/0x1b0
[ 172.487172] Modules linked in:
[ 172.488911] CPU: 3 UID: 0 PID: 728318 Comm: 291 Not tainted 6.12.0-rc5-dgc+ #273
[ 172.492022] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 172.496029] RIP: 0010:pick_task_fair+0xb6/0x1b0
[ 172.497978] Code: 40 f3 f3 03 01 74 2a 41 80 7f 50 00 74 96 f6 05 31 f3 f3 03 01 75 8d c6 05 28 f3 f3 03 01 48 c7 c7 41 26 e4 82 e8 7a d7 fa ff <0f> 0b e9 73 ff ff ff c6 05 0d f3 f3 03 01 48 c7 c7 2f 26 e4 82 e8
[ 172.505868] RSP: 0018:ffffc9002ec83d60 EFLAGS: 00010046
[ 172.508111] RAX: bdcdd05ee831a400 RBX: 0000000000000000 RCX: 0000000000000027
[ 172.511139] RDX: 0000000000000000 RSI: 00000000ffdfffff RDI: ffff88881fadc9c8
[ 172.514326] RBP: ffffc9002ec83d88 R08: 00000000001fffff R09: ffff88a018a00000
[ 172.517804] R10: 00000000005ffffd R11: 0000000000000004 R12: ffff888122b58c00
[ 172.520788] R13: ffff88881faf0140 R14: ffff88881faf00c0 R15: ffff88819e8cd180
[ 172.523748] FS: 0000000000000000(0000) GS:ffff88881fac0000(0000) knlGS:0000000000000000
[ 172.527167] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 172.529571] CR2: 00007f378e8866fc CR3: 000000104daae000 CR4: 0000000000350ef0
[ 172.532601] Call Trace:
[ 172.533666] <TASK>
[ 172.534557] ? show_regs+0x5e/0x70
[ 172.535993] ? __warn+0xd0/0x1d0
[ 172.537430] ? pick_task_fair+0xb6/0x1b0
[ 172.539062] ? report_bug+0x145/0x1f0
[ 172.540619] ? handle_bug+0x67/0x90
[ 172.542060] ? exc_invalid_op+0x1b/0x50
[ 172.543854] ? asm_exc_invalid_op+0x1b/0x20
[ 172.545688] ? pick_task_fair+0xb6/0x1b0
[ 172.547353] pick_next_task_fair+0x27/0x330
[ 172.549090] __schedule+0x2ad/0xb10
[ 172.550460] do_task_dead+0x43/0x50
[ 172.551743] do_exit+0x836/0xab0
[ 172.552950] do_group_exit+0x8f/0x90
[ 172.554274] __x64_sys_exit_group+0x17/0x20
[ 172.555808] x64_sys_call+0x2ed3/0x2ee0
[ 172.557210] do_syscall_64+0x68/0x130
[ 172.558531] ? exc_page_fault+0x62/0xc0
[ 172.559907] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 172.561739] RIP: 0033:0x7f378e74b3c5
[ 172.563036] Code: Unable to access opcode bytes at 0x7f378e74b39b.
[ 172.565278] RSP: 002b:00007ffd21861488 EFLAGS: 00000206 ORIG_RAX: 00000000000000e7
[ 172.568001] RAX: ffffffffffffffda RBX: 00007f378e857fa8 RCX: 00007f378e74b3c5
[ 172.570589] RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000000
[ 172.573182] RBP: 0000000000000000 R08: 00007ffd21861428 R09: 00007ffd218613af
[ 172.575758] R10: 00007ffd21861320 R11: 0000000000000206 R12: 00007f378e856680
[ 172.578356] R13: 00007f378e8b9f40 R14: 0000000000000001 R15: 00007f378e857fc0
[ 172.580941] </TASK>
There was nothing particularly obvious that caused it. It's a 64p
VM, running a heavy concurrent fstests workload that takes about 20
minutes to complete. There are a bit over 8000 tasks reported, most
of them kernel threads. The load is consuming about 50 CPUs, 40GB of
RAM, sustaining ~3GB/s of IO to/from disk across about 130 block
devices and the scheduler is context switching around 800,000 times
a second.
I have no idea how to reproduce this on demand - it randomly shows
up in about 1 in every 10 test runs and all the tests running at
that point in time report failure because they all detect this
warning in dmesg.
I have not been able to test v6.12-rc5 yet.
Can you share your config? And/Or compare to mine at
https://pastebin.com/Y7DXnMG2
Maybe we can see what was merged for the sched in 6.12, and I can try
before and after. I don't like the prospect of a full bisect.
Thanks,
John