Re: [BUG] Splat during modest hazptrtorture run

[Mathieu Desnoyers]

On 2026-10-07 11:59, Paul E. McKenney wrote:
> On Wed, Oct 07, 2026 at 03:09:27AM -0400, Mathieu Desnoyers wrote:
> > On 2026-10-06 19:40, Paul E. McKenney wrote:
> > > Hello!
> > >
> > > This is all new code, so the bug could be anywhere.  So you all need
> > > to know.  ;-)
> > >
> > > I got this from the NOPREEMPT variant of hazptr during a nominal
> > > "--duration 60" run of torture.sh on x86 with the guest OS split across
> > > two NUMA nodes:
> > >
> > > [  137.765104] WARNING: kernel/rcu/hazptrtorture.c:658 at hazptr_torture_stats_print+0x25b/0x4f0, CPU#1: hazptr_torture_/136
> > > [  137.768647] Modules linked in:
> > > [  137.768891] CPU: 1 UID: 0 PID: 136 Comm: hazptr_torture_ Not tainted 7.3.0-rc5-00661-ga1f1e4890d1d-dirty #193 PREEMPTLAZY
> > > [  137.769683] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-6.el9 11/05/2023
> > > [  137.770319] RIP: 0010:hazptr_torture_stats_print+0x25b/0x4f0
> > > [  137.770735] Code: 48 83 c4 20 e8 86 44 fe ff 41 83 fd 01 7e 23 48 c7 c6 6e 85 17 b0 48 c7 c7 db 27 17 b0 e8 6d 44 fe ff f0 ff 05 76 6e 0a 02 90 <0f> 0b 90 4c 8b 64 24 70 48 c7 c7 73 85 17 b0 e8 51 44 fe ff 48 8b
> > > [  137.772061] RSP: 0018:ffffa738004ffdf0 EFLAGS: 00010202
> > > [  137.772435] RAX: 0000000000000004 RBX: ffffa738004ffe08 RCX: 0000000000000027
> > > [  137.772950] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
> > > [  137.773455] RBP: ffffa738004ffe60 R08: 4000000000001236 R09: ffffffffb01727df
> > > [  137.773980] R10: 0000000020212121 R11: 0000000020212121 R12: 0000000000000000
> > > [  137.774479] R13: 0000000000000002 R14: 000000000002ffd6 R15: 0000000000034f03
> > > [  137.775000] FS:  0000000000000000(0000) GS:ffff999c2e502000(0000) knlGS:0000000000000000
> > > [  137.775578] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [  137.776001] CR2: 0000000000000000 CR3: 0000000008830000 CR4: 00000000000006f0
> > > [  137.776512] Call Trace:
> > > [  137.776700]  <TASK>
> > > [  137.776863]  ? __pfx_hazptr_torture_stats+0x10/0x10
> > > [  137.777207]  hazptr_torture_stats+0x25/0x70
> > > [  137.777508]  kthread+0xd9/0x110
> > > [  137.777751]  ? __pfx_kthread+0x10/0x10
> > > [  137.778017]  ret_from_fork+0x1bd/0x220
> > > [  137.778285]  ? __pfx_kthread+0x10/0x10
> > > [  137.778560]  ret_from_fork_asm+0x1a/0x30
> > > [  137.778849]  </TASK>
> > > [  137.779007] ---[ end trace 0000000000000000 ]---
> > >
> > > I have not yet seen this during a PREEMPT run.  Line 658 of
> > > hazptrtorture.c is the WARN_ON_ONCE() below:
> > >
> > > 	if (i > 1) {
> > > 		pr_cont("%s", "!!! ");
> > > 		atomic_inc(&n_hazptr_torture_error);
> > > 		WARN_ON_ONCE(i > 1); // Too-short grace period
> > > 	}
> > >
> > > Any thoughts on what might be causing this?
> >
> > Hi Paul!
> >
> > Can you share which tree and branch (commit) this is running ?
> >
> > Does it include my fix from this series ? That would be patch 1 of:
> >
> > https://lore.kernel.org/lkml/20260927155134.4740-1-mathieu.desnoyers@xxxxxxxxxxxx/
>
> Ah, no, I somehow got the impression that this series was going to be
> updated, so did not apply it.  Apologies!
>
> I will pull these in.

About the patches introducing ptr_eq(), I plan to handle Linus' feedback
perhaps in an additional patch and have the "generic" ptr_eq()
implemented under asm-generic, and a x86-specific implementation of it
in assembly. Are you OK with this being a follow up or would you prefer
I fold this in the original patch ?

> > Does it run the additional series from Kunwu Chan found at
> > https://lore.kernel.org/lkml/20261002170847.3653663-1-kunwu.chan@xxxxxxxxx/ ?
>
> No, but if you are good with it I will pull it in.
>
> May I add your Acked-by or Reviewed-by?

With LPC going on, I did not have time to review it, sorry. Not yet
please.

Thanks,

Mathieu

> 							Thanx, Paul
>
> > Thanks,
> >
> > Mathieu
> >
> > > For that matter, can anyone else reproduce this?
> > >
> > > 								Thanx, Paul
> >
> >
> > --
> > Mathieu Desnoyers
> > EfficiOS Inc.
> > https://www.efficios.com


--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com