linux-kernel - Re: [patch V3 00/20] sched: Rewrite MM CID management

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Message-ID: <87ecqisw2h.ffs@tglx>
Date: Fri, 31 Oct 2025 20:36:06 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>, LKML
 <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Gabriele Monaco
 <gmonaco@...hat.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Michael Jeanson <mjeanson@...icios.com>, Jens Axboe <axboe@...nel.dk>,
 "Paul E. McKenney" <paulmck@...nel.org>, "Gautham R. Shenoy"
 <gautham.shenoy@....com>, Florian Weimer <fweimer@...hat.com>, Tim Chen
 <tim.c.chen@...el.com>, Yury Norov <yury.norov@...il.com>
Subject: Re: [patch V3 00/20] sched: Rewrite MM CID management

On Thu, Oct 30 2025 at 12:10, Shrikanth Hegde wrote:
>> I am running into crash at boot on power10 pseries.
>> Thought of putting it here first. Me trying to figure out why.
>> 
>> I am using your tree.
>> git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git

Can you update and revalidate? There are a couple of fixes there though
I don't know how they would be related.

>> Oops: Kernel access of bad area, sig: 7 [#3]
>> LE PAGE_SIZE=64K MMU=Radix  SMP NR_CPUS=8192 NUMA pSeries
>> Modules linked in: drm drm_panel_orientation_quirks xfs sd_mod sg 
>> ibmvscsi ibmveth scsi_transport_srp pseries_wdt dm_mirror dm_region_hash 
>> dm_log dm_mod fuse
>> CPU: 96 UID: 0 PID: 0 Comm: swapper/96 Tainted: G      D W           
>> 6.18.0-rc3+ #4 PREEMPT(lazy)
>> Tainted: [D]=DIE, [W]=WARN
>> NIP [c0000000001b5c10] mm_cid_switch_to+0x58/0x52c

If it happens again, can you decode the source line?

>> LR [c000000001117c84] __schedule+0x4bc/0x760
>> Call Trace:
>> [c00000668367fde0] [c0000000001b53c8] __pick_next_task+0x60/0x2ac 
>> (unreliable)
>> [c00000668367fe40] [c000000001117a14] __schedule+0x24c/0x760
>> [c00000668367fee0] [c0000000011183d0] schedule_idle+0x3c/0x64
>> [c00000668367ff10] [c0000000001f2470] do_idle+0x15c/0x1ac
>> [c00000668367ff60] [c0000000001f2788] cpu_startup_entry+0x4c/0x50
>> [c00000668367ff90] [c00000000005ef20] start_secondary+0x284/0x288
>> [c00000668367ffe0] [c00000000000e158] start_secondary_prolog+0x10/0x14
>> 
>
> Issue happens with NR_CPUS=8192. System boots fine with NR_CPUS=2048

Hmm. Let me build a kernel with 8K and throw it at a VM then.

Thanks,

        tglx