linux-kernel - Re: [patch V3 00/12] rseq: Implement time slice extension mechanism

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Message-ID: <03687B00-0194-4707-ABCB-FB3CD5340F11@oracle.com>
Date: Thu, 6 Nov 2025 17:28:52 +0000
From: Prakash Sangappa <prakash.sangappa@...cle.com>
To: Thomas Gleixner <tglx@...utronix.de>
CC: LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra
	<peterz@...radead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, Jonathan Corbet <corbet@....net>,
        Madadi Vineeth Reddy
	<vineethr@...ux.ibm.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Steven
 Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior
	<bigeasy@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [patch V3 00/12] rseq: Implement time slice extension mechanism



> On Oct 29, 2025, at 6:22 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> This is a follow up on the V2 version:
> 
>     https://lore.kernel.org/20251022110646.839870156@linutronix.de
> 
> V1 contains a detailed explanation:
> 
>     https://lore.kernel.org/20250908225709.144709889@linutronix.de
> 
> TLDR: Time slice extensions are an attempt to provide opportunistic
> priority ceiling without the overhead of an actual priority ceiling
> protocol, but also without the guarantees such a protocol provides.

[…]
> 
> 
> The uaccess and RSEQ modifications on which this series is based can be
> found here:
> 
>    https://lore.kernel.org/20251029123717.886619142@linutronix.de
> 
> and in git:
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/cid
> 
> For your convenience all of it is also available as a conglomerate from
> git:
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/slice
> 

Hit this watchdog panic.

Using following tree. Assume this Is the latest.
https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/ rseq/slice

Appears to be spinning in mm_get_cid(). Must be the mm cid changes.
https://lore.kernel.org/all/20251029123717.886619142@linutronix.de/

-Prakash
-------------------------------------------------------
watchdog: CPU152: Watchdog detected hard LOCKUP on cpu 152
..  

93.093858] RIP: 0010:mm_get_cid+0x7e/0xd0
[   93.093866] Code: 4c eb 63 f3 90 8b 05 f1 6a 66 02 8b 35 d7 bc 8e 01 83 c0 3f 48 89 f5 c1 e8 03 25 f8 ff ff 1f 48 8d 3c 43 e8 24 ce 62 00 89 c1 <39> e8 73 d5 8b 35 c8 6a 66 02 89 c0 8d 56 3f c1 ea 03 81 e2 f8 ff
[   93.093867] RSP: 0018:ff734c4591c6bc38 EFLAGS: 00000046
[   93.093869] RAX: 0000000000000180 RBX: ff3c42cea15ec2c0 RCX: 0000000000000180
[   93.093871] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[   93.093872] RBP: 0000000000000180 R08: 0000000000000000 R09: 0000000000000000
[   93.093873] R10: 0000000000000000 R11: 00000000fffffff4 R12: ff3c42cea15ebd30
[   93.093874] R13: ffa54c453ba41640 R14: ff3c42cea15ebd28 R15: ff3c42cea15ebd27
[   93.093875] FS:  00007f92b1482740(0000) GS:ff3c43e8d55ef000(0000) knlGS:0000000000000000
[   93.093876] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   93.093877] CR2: 00007f8ebe7fbfb8 CR3: 00000126c9f61004 CR4: 0000000000f71ef0
[   93.093878] PKRU: 55555554
[   93.093879] Call Trace:
[   93.093882]  <TASK>
[   93.093887]  sched_mm_cid_fork+0x22d/0x300
[   93.093895]  copy_process+0x92a/0x1670
[   93.093902]  kernel_clone+0xbc/0x490
[   93.093903]  ? srso_alias_return_thunk+0x5/0xfbef5
[   93.093907]  ? __lruvec_stat_mod_folio+0x83/0xd0
[   93.093911]  __do_sys_clone+0x65/0xa0
[   93.093916]  do_syscall_64+0x7f/0x8a0

> Thanks,
> 
> tglx
>