Re: [syzbot] [kernel?] WARNING in update_curr_idle

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jun 12, 2026 at 11:10:23AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ec039126b7fa Add linux-next specific files for 20260611
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14d128ae580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5aaa5302b37e7e10
> dashboard link: https://syzkaller.appspot.com/bug?extid=e671c2192fed8645642e
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/4f58c704a9e9/disk-ec039126.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/bf67100d5618/vmlinux-ec039126.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/bf93fe076f41/bzImage-ec039126.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e671c2192fed8645642e@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> rq->clock_update_flags < RQCF_ACT_SKIP
> WARNING: kernel/sched/sched.h:1792 at assert_clock_updated kernel/sched/sched.h:1792 [inline], CPU#1: swapper/1/0
> WARNING: kernel/sched/sched.h:1792 at rq_clock_task kernel/sched/sched.h:1806 [inline], CPU#1: swapper/1/0
> WARNING: kernel/sched/sched.h:1792 at update_curr_idle+0x1cf/0x260 kernel/sched/idle.c:554, CPU#1: swapper/1/0
> Modules linked in:
> CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
> Tainted: [L]=SOFTLOCKUP
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
> RIP: 0010:assert_clock_updated kernel/sched/sched.h:1792 [inline]
> RIP: 0010:rq_clock_task kernel/sched/sched.h:1806 [inline]
> RIP: 0010:update_curr_idle+0x1cf/0x260 kernel/sched/idle.c:554
> Code: e8 03 42 80 3c 20 00 74 08 48 89 df e8 3a 98 97 00 48 8b 3b 4c 89 f6 4c 89 fa 5b 41 5c 41 5d 41 5e 41 5f 5d e9 52 38 01 00 90 <0f> 0b 90 e9 01 ff ff ff 90 0f 0b 90 e9 d3 fe ff ff 48 c7 c1 40 84
> RSP: 0018:ffffc900001e7bf8 EFLAGS: 00010097
> RAX: 0000000000000000 RBX: ffff8880b873ba40 RCX: 0000000000000002
> RDX: ffff888037668000 RSI: ffffffff8d8bd52f RDI: ffffffff8baa5680
> RBP: ffffc900001e7e30 R08: ffff8880b873c91f R09: 0000000000000000
> R10: ffff8880b873c910 R11: ffffffff8199c020 R12: dffffc0000000000
> R13: ffffffff8d8f3158 R14: ffff88801da9dd00 R15: ffff8880b873c620
> FS:  0000000000000000(0000) GS:ffff888125fb8000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000110c42f07e CR3: 0000000040078000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  put_prev_task_idle+0xd/0x20 kernel/sched/idle.c:485
>  put_prev_set_next_task kernel/sched/sched.h:2769 [inline]
>  pick_next_task kernel/sched/core.c:6442 [inline]
>  __schedule+0x3da0/0x5550 kernel/sched/core.c:7143
>  schedule_idle+0x51/0x90 kernel/sched/core.c:7348
>  do_idle+0x4a6/0x540 kernel/sched/idle.c:384
>  cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:454
>  start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:312
>  common_startup_64+0x13e/0x157
>  </TASK>
> 
> 
> ---
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> #syz fix: exact-commit-title

While this looks a bit different from the known reports, it might be the
same since the config has SCHED_CORE=y

#syz fix: c095741713d1 sched/fair: Fix newidle vs core-sched