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

[syzbot]

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+484ec8...@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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[Peter Zijlstra]

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