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

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Message-ID: <ae8de225-3c07-43ac-80d1-ecb6ac45d5d9@linux.ibm.com>
Date: Thu, 30 Oct 2025 12:10:30 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Thomas Gleixner <tglx@...utronix.de>, 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 10/30/25 10:30 AM, Shrikanth Hegde wrote:
> Hi Thomas.

>> +----------------------
>>   kernel/sched/sched.h           |  395 ++++++++-----------
>>   kernel/signal.c                |    2
>>   lib/bitmap.c                   |    6
>>   16 files changed, 727 insertions(+), 823 deletions(-)
>>
>>
> 
> 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
> 
> commit 789ff6e7cc5aa423473eb135f94812fe77b8aeab (HEAD -> rseq/cid, 
> origin/rseq/cid)
> Author: Thomas Gleixner <tglx@...utronix.de>
> Date:   Tue Oct 14 10:51:04 2025 +0200
> 
>      sched/mmcid: Switch over to the new mechanism
> 
> 
> 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
> 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