Re: [syzbot] [kernel?] general protection fault in __schedule (3)

[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=137c78ae580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5aaa5302b37e7e10
> dashboard link: https://syzkaller.appspot.com/bug?extid=484ec80b3ff2dbdea632
> 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+484ec80b3ff2dbdea632@syzkaller.appspotmail.com
> 
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
> CPU: 0 UID: 0 PID: 5884 Comm: syz.2.21 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
> RIP: 0010:task_cpu include/linux/sched.h:2268 [inline]
> RIP: 0010:is_task_rq_idle kernel/sched/core.c:6169 [inline]
> RIP: 0010:cookie_equals kernel/sched/core.c:6174 [inline]
> RIP: 0010:pick_next_task kernel/sched/core.c:6355 [inline]
> RIP: 0010:__schedule+0x4030/0x5550 kernel/sched/core.c:7143
> Code: 24 80 00 00 00 e8 80 67 fc f6 48 8b 84 24 80 00 00 00 48 8b 18 4c 8d 7b 14 4c 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 87 04 00 00 45 8b 3f 49 83 ff 08 0f 83 98
> RSP: 0000:ffffc9000565fcc0 EFLAGS: 00010003
> RAX: 0000000000000002 RBX: 0000000000000000 RCX: dffffc0000000000
> RDX: 0000000000000003 RSI: 0000000000000000 RDI: ffff8880b8620c60
> RBP: ffffc9000565fea8 R08: ffffffff8f8d70f7 R09: 1ffffffff1f1ae1e
> R10: dffffc0000000000 R11: fffffbfff1f1ae1f R12: ffff8880b863c658
> R13: ffff888125eb8000 R14: 1ffff110170c7922 R15: 0000000000000014
> FS:  000055557157d500(0000) GS:ffff888125eb8000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555904597d0 CR3: 000000005f3e8000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  __schedule_loop kernel/sched/core.c:7307 [inline]
>  schedule+0x164/0x360 kernel/sched/core.c:7322
>  __exit_to_user_mode_loop kernel/entry/common.c:55 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:101 [inline]
>  __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
>  irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:244 [inline]
>  irqentry_exit_to_user_mode include/linux/irq-entry-common.h:315 [inline]
>  irqentry_exit+0x291/0x8c0 kernel/entry/common.c:165
>  asm_sysvec_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:679
> RIP: 0033:0x7f9b0e311494
> Code: 54 24 28 0f 82 5e 03 00 00 40 0f b6 fe c6 44 24 0e 01 45 31 ed 45 31 f6 89 7c 24 08 85 c0 0f 84 10 01 00 00 66 90 48 8b 3c 24 <49> 8b 54 24 40 4c 89 f0 4a 03 14 ef 80 3d 01 69 3a 00 00 49 89 d6
> RSP: 002b:00007fff0de8b200 EFLAGS: 00000293
> RAX: 0000000000000001 RBX: ffffffff81b962a3 RCX: ffffffff81b962a3
> RDX: 00000000000002a3 RSI: ffffffff81b962a3 RDI: 00007f9b0da95008
> RBP: 0000000000000000 R08: 00007f9b0e6a0000 R09: 00007f9b0e6a2000
> R10: 0000000081b962a7 R11: 0000000000000006 R12: 00007f9b0e6b6128
> R13: 000000000000a5e4 R14: ffffffff81b96705 R15: 00007f9b0f1e5720
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:task_cpu include/linux/sched.h:2268 [inline]
> RIP: 0010:is_task_rq_idle kernel/sched/core.c:6169 [inline]
> RIP: 0010:cookie_equals kernel/sched/core.c:6174 [inline]
> RIP: 0010:pick_next_task kernel/sched/core.c:6355 [inline]
> RIP: 0010:__schedule+0x4030/0x5550 kernel/sched/core.c:7143
> Code: 24 80 00 00 00 e8 80 67 fc f6 48 8b 84 24 80 00 00 00 48 8b 18 4c 8d 7b 14 4c 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 87 04 00 00 45 8b 3f 49 83 ff 08 0f 83 98
> RSP: 0000:ffffc9000565fcc0 EFLAGS: 00010003
> RAX: 0000000000000002 RBX: 0000000000000000 RCX: dffffc0000000000
> RDX: 0000000000000003 RSI: 0000000000000000 RDI: ffff8880b8620c60
> RBP: ffffc9000565fea8 R08: ffffffff8f8d70f7 R09: 1ffffffff1f1ae1e
> R10: dffffc0000000000 R11: fffffbfff1f1ae1f R12: ffff8880b863c658
> R13: ffff888125eb8000 R14: 1ffff110170c7922 R15: 0000000000000014
> FS:  000055557157d500(0000) GS:ffff888125eb8000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555904597d0 CR3: 000000005f3e8000 CR4: 00000000003526f0
> ----------------
> Code disassembly (best guess):
>    0:	24 80                	and    $0x80,%al
>    2:	00 00                	add    %al,(%rax)
>    4:	00 e8                	add    %ch,%al
>    6:	80 67 fc f6          	andb   $0xf6,-0x4(%rdi)
>    a:	48 8b 84 24 80 00 00 	mov    0x80(%rsp),%rax
>   11:	00
>   12:	48 8b 18             	mov    (%rax),%rbx
>   15:	4c 8d 7b 14          	lea    0x14(%rbx),%r15
>   19:	4c 89 f8             	mov    %r15,%rax
>   1c:	48 c1 e8 03          	shr    $0x3,%rax
>   20:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
>   27:	fc ff df
> * 2a:	0f b6 04 08          	movzbl (%rax,%rcx,1),%eax <-- trapping instruction
>   2e:	84 c0                	test   %al,%al
>   30:	0f 85 87 04 00 00    	jne    0x4bd
>   36:	45 8b 3f             	mov    (%r15),%r15d
>   39:	49 83 ff 08          	cmp    $0x8,%r15
>   3d:	0f                   	.byte 0xf
>   3e:	83                   	.byte 0x83
>   3f:	98                   	cwtl
> 
> 
> ---
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> 
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> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title

Both these reports are SCHED_CORE=y and there was a known issue there,
which should be fixed in today's edition (next-20260612) with commit:

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