Re: [syzbot] [kernel?] WARNING in update_rq_clock (2)

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 03, 2026 at 11:39:38AM +0200, Thomas Gleixner wrote:
> On Thu, Jul 02 2026 at 17:38, syzbot wrote:
> 
> CC+: Peter
> 
> Dear syzbot folks. The selection of people you CC on your reports is
> annoyingly random. The splat clearly says:
> 
> > WARNING: kernel/sched/sched.h:1641 at lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline], CPU#0: syz.4.1183/11558
> 
> So why not picking that up and:
> 
> # scripts/get_maintainer.pl -f kernel/sched/sched.h 
> 
> Ingo Molnar <mingo@redhat.com> (maintainer:SCHEDULER)
> Peter Zijlstra <peterz@infradead.org> (maintainer:SCHEDULER)
> Juri Lelli <juri.lelli@redhat.com> (maintainer:SCHEDULER)
> Vincent Guittot <vincent.guittot@linaro.org> (maintainer:SCHEDULER)
> Dietmar Eggemann <dietmar.eggemann@arm.com> (reviewer:SCHEDULER)
> Steven Rostedt <rostedt@goodmis.org> (reviewer:SCHEDULER)
> Ben Segall <bsegall@google.com> (reviewer:SCHEDULER)
> Mel Gorman <mgorman@suse.de> (reviewer:SCHEDULER)
> Valentin Schneider <vschneid@redhat.com> (reviewer:SCHEDULER)
> K Prateek Nayak <kprateek.nayak@amd.com> (reviewer:SCHEDULER)
> linux-kernel@vger.kernel.org (open list:SCHEDULER)
> 
> 
> ?
> 
> Leaving the report untrimmed for Peter.
> 
> > syzbot found the following issue on:
> >
> > HEAD commit:    8b69c0475871 Merge tag 'input-for-v7.2-rc0-2' of git://git..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1196f4ea580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=eb3cf873145f98c4
> > dashboard link: https://syzkaller.appspot.com/bug?extid=681e729b2cf0d4860042
> > compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/6fbba2b94559/disk-8b69c047.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/377e82061e2d/vmlinux-8b69c047.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/f299b46fb771/bzImage-8b69c047.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+681e729b2cf0d4860042@syzkaller.appspotmail.com
> >
> > ------------[ cut here ]------------
> > debug_locks && !(lock_is_held(&(__rq_lockp(rq))->dep_map) != 0)
> > WARNING: kernel/sched/sched.h:1641 at lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline], CPU#0: syz.4.1183/11558
> > WARNING: kernel/sched/sched.h:1641 at lockdep_assert_rq_held kernel/sched/sched.h:1638 [inline], CPU#0: syz.4.1183/11558
> > WARNING: kernel/sched/sched.h:1641 at update_rq_clock+0x40a/0xd20 kernel/sched/core.c:865, CPU#0: syz.4.1183/11558
> > Modules linked in:
> > CPU: 0 UID: 0 PID: 11558 Comm: syz.4.1183 Tainted: G     U       L      syzkaller #0 PREEMPT(full) 
> > Tainted: [U]=USER, [L]=SOFTLOCKUP
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
> > RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1641 [inline]
> > RIP: 0010:lockdep_assert_rq_held kernel/sched/sched.h:1638 [inline]
> > RIP: 0010:update_rq_clock+0x40a/0xd20 kernel/sched/core.c:865
> > Code: ab c8 0b 00 00 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f e9 d8 7e c8 09 a8 04 0f 84 df fc ff ff 90 0f 0b 90 e9 d6 fc ff ff 90 <0f> 0b 90 e9 92 fc ff ff 4c 8d 83 c0 0b 00 00 48 b8 00 00 00 00 00
> > RSP: 0018:ffffc90003cb70b8 EFLAGS: 00010046
> > RAX: 0000000000000000 RBX: ffff8880b853b600 RCX: 0000000000000001
> > RDX: 0000000000000046 RSI: ffffffff8df333b0 RDI: ffffffff8c1e8f80
> > RBP: ffffc90003cb7260 R08: 0000000000000001 R09: 0000000000000001
> > R10: ffffffff90dbdb97 R11: 0000000000000000 R12: ffffffff90dc0f44
> > R13: ffff8880b853c4e0 R14: ffff88801e6a1f00 R15: ffff8880b843c198
> > FS:  00007fece89b36c0(0000) GS:ffff8881242e7000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000000 CR3: 00000000775a2000 CR4: 00000000003526f0
> > Call Trace:
> >  <TASK>
> >  pick_next_task kernel/sched/core.c:6338 [inline]
> >  __schedule+0x1e2d/0x6730 kernel/sched/core.c:7149

This doesn't really make sense, this is in SCHED_CORE's pick_next_task()
restart_multi: loop. It does update_rq_clock() for all 'other' SMT
siblings, and validates __rq_lockp(rq) is held, which it very much
should be there.

Given you don't have a reproducer, and the static lock context analysis
code isn't complaining here, I'm rather suspect of the report and would
not rule out random memory corruption.

Anyway, if this persists and or a reproducer is found, I'm sure I'll
look at it eventually.