linux-kernel - [BUG] Kernel panic in __migrate_swap_task() on 6.16-rc2 (NULL pointer dereference)

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Message-ID: <CAE4VaGBLJxpd=NeRJXpSCuw=REhC5LWJpC29kDy-Zh2ZDyzQZA@mail.gmail.com>
Date: Tue, 17 Jun 2025 22:05:30 +0200
From: Jirka Hladky <jhladky@...hat.com>
To: linux-kernel <linux-kernel@...r.kernel.org>
Subject: [BUG] Kernel panic in __migrate_swap_task() on 6.16-rc2 (NULL pointer dereference)

Hi all,

I’ve encountered a reproducible kernel panic on 6.16-rc1 and 6.16-rc2
involving a NULL pointer dereference in `__migrate_swap_task()` during
CPU migration. This occurred on various AMD and Intel systems while
running a CPU-intensive workload (Linpack, Stress_ng - it's not
specific to a benchmark).

Full trace below:
---
BUG: kernel NULL pointer dereference, address: 00000000000004c8
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 4078b99067 P4D 4078b99067 PUD 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 74 UID: 0 PID: 466 Comm: migration/74 Kdump: loaded Not tainted
6.16.0-0.rc2.24.eln149.x86_64 #1 PREEMPT(lazy)
Hardware name: GIGABYTE R182-Z91-00/MZ92-FS0-00, BIOS M07 09/03/2021
Stopper: multi_cpu_stop+0x0/0x130 <- migrate_swap+0xa7/0x120
RIP: 0010:__migrate_swap_task+0x2f/0x170
Code: 41 55 4c 63 ee 41 54 55 53 48 89 fb 48 83 87 a0 04 00 00 01 65
48 ff 05 e7 14 dd 02 48 8b af 50 0a 00 00 66 90 e8 61 93 07 00 <48> 8b
bd c8 04 00 00 e8 85 11 35 00 48 85 c0 74 12 ba 01 00 00 00
RSP: 0018:ffffce79cd90bdd0 EFLAGS: 00010002
RAX: 0000000000000001 RBX: ffff8e9c7290d1c0 RCX: 0000000000000000
RDX: ffff8e9c71e83680 RSI: 000000000000001b RDI: ffff8e9c7290d1c0
RBP: 0000000000000000 R08: 00056e36392913e7 R09: 00000000002ab980
R10: ffff8eac2fcb13c0 R11: ffff8e9c77997410 R12: ffff8e7c2fcf12c0
R13: 000000000000001b R14: ffff8eac71eda944 R15: ffff8eac71eda944
FS:  0000000000000000(0000) GS:ffff8eac9db4a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000004c8 CR3: 0000003072388003 CR4: 0000000000f70ef0
PKRU: 55555554
Call Trace:
 <TASK>
 migrate_swap_stop+0xe8/0x190
 multi_cpu_stop+0xf3/0x130
 ? __pfx_multi_cpu_stop+0x10/0x10
 cpu_stopper_thread+0x97/0x140
 ? __pfx_smpboot_thread_fn+0x10/0x10
 smpboot_thread_fn+0xf3/0x220
 kthread+0xfc/0x240
 ? __pfx_kthread+0x10/0x10
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0xf0/0x110
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>
---

**Kernel Version:**
6.16.0-0.rc2.24.eln149.x86_64 (Fedora rawhide)
https://koji.fedoraproject.org/koji/buildinfo?buildID=2732950

**Reproducibility:**
Happened multiple times during routine CPU-intensive operations. It
happens with various benchmarks (Stress_ng, Linpack) after several
hours of performance testing. `migration/*` kernel threads hit a NULL
dereference in `__migrate_swap_task`.

**System Info:**
- Platform: GIGABYTE R182-Z91-00 (dual socket EPYC)
- BIOS: M07 09/03/2021
- Config: Based on Fedora’s debug kernel (`PREEMPT(lazy)`)

**Crash Cause (tentative):**
NULL dereference at offset `0x4c8` from a task struct pointer in
`__migrate_swap_task`. Possibly an uninitialized or freed
`task_struct` field.

Please let me know if you’d like me to test a patch or if you need
more details.

Thanks,
Jirka