[syzbot ci] Re: Implement a new generic pagewalk API

[syzbot ci]

syzbot ci has tested the following series

[v3] Implement a new generic pagewalk API
https://lore.kernel.org/all/20260525165528.1...@suse.de
* [RFC PATCH v3 1/8] mm: Add softleaf_from_pud
* [RFC PATCH v3 2/8] mm: Add {pmd,pud}_huge_lock helper
* [RFC PATCH v3 3/8] mm: Implement folio_pmd_batch
* [RFC PATCH v3 4/8] mm: Implement pt_range_walk
* [RFC PATCH v3 5/8] mm: Make /proc/pid/smaps use the new generic pagewalk API
* [RFC PATCH v3 6/8] mm: Make /proc/pid/numa_maps use the new generic pagewalk API
* [RFC PATCH v3 7/8] mm: Make /proc/pid/pagemap use the new generic pagewalk API
* [RFC PATCH v3 8/8] mm: Make /proc/pid/clear_refs use the new generic pagewalk API

and found the following issue:
general protection fault in clear_refs_write

Full report is available here:
https://ci.syzbot.org/series/0beab2d0-9d88-4288-ac81-b294e51c057d

***

general protection fault in clear_refs_write

tree: mm-new
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base: 5200f5f493f79f14bbdc349e402a40dfb32f23c8
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/8f20e88b-808c-4c60-9b8e-0af4c9fce5ff/config
syz repro: https://ci.syzbot.org/findings/634b1f0a-cf64-4607-928a-ef3ad40f765c/syz_repro

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 UID: 0 PID: 5863 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:clear_soft_dirty_pmd fs/proc/task_mmu.c:1545 [inline]
RIP: 0010:clear_refs_pmd_range fs/proc/task_mmu.c:1581 [inline]
RIP: 0010:clear_refs_write+0xaa7/0x1590 fs/proc/task_mmu.c:1721
Code: 44 24 10 4c 8b bc 24 20 02 00 00 83 7c 24 28 04 0f 85 aa 05 00 00 48 8b 9c 24 08 02 00 00 48 89 d8 48 c1 e8 03 48 89 44 24 58 <42> 80 3c 20 00 74 08 48 89 df e8 fa 2c c6 ff 4c 8b 23 4c 89 e6 48
RSP: 0018:ffffc900037bf960 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000005
RDX: ffffffff826b21ce RSI: ffffffff8eb17b50 RDI: 0000000000000001
RBP: ffffc900037bfc10 R08: ffff8881047c0000 R09: 0000000000000002
R10: 0000000000000002 R11: 0000000000000000 R12: dffffc0000000000
R13: fffff520006f7f40 R14: ffff8881141c8308 R15: ffff8881141c8300
FS: 00007ff8ffc1d6c0(0000) GS:ffff8882a928a000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33e63fff CR3: 000000010476e000 CR4: 00000000000006f0
Call Trace:
<TASK>
do_loop_readv_writev fs/read_write.c:852 [inline]
vfs_writev+0x4bd/0x990 fs/read_write.c:1061
do_writev+0x154/0x2e0 fs/read_write.c:1105
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff8fed9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff8ffc1d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007ff8ff015fa0 RCX: 00007ff8fed9ce59
RDX: 0000000000000001 RSI: 00002000000000c0 RDI: 0000000000000003
RBP: 00007ff8fee32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff8ff016038 R14: 00007ff8ff015fa0 R15: 00007fffd02796e8
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:clear_soft_dirty_pmd fs/proc/task_mmu.c:1545 [inline]
RIP: 0010:clear_refs_pmd_range fs/proc/task_mmu.c:1581 [inline]
RIP: 0010:clear_refs_write+0xaa7/0x1590 fs/proc/task_mmu.c:1721
Code: 44 24 10 4c 8b bc 24 20 02 00 00 83 7c 24 28 04 0f 85 aa 05 00 00 48 8b 9c 24 08 02 00 00 48 89 d8 48 c1 e8 03 48 89 44 24 58 <42> 80 3c 20 00 74 08 48 89 df e8 fa 2c c6 ff 4c 8b 23 4c 89 e6 48
RSP: 0018:ffffc900037bf960 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000005
RDX: ffffffff826b21ce RSI: ffffffff8eb17b50 RDI: 0000000000000001
RBP: ffffc900037bfc10 R08: ffff8881047c0000 R09: 0000000000000002
R10: 0000000000000002 R11: 0000000000000000 R12: dffffc0000000000
R13: fffff520006f7f40 R14: ffff8881141c8308 R15: ffff8881141c8300
FS: 00007ff8ffc1d6c0(0000) GS:ffff8882a928a000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b34063fff CR3: 000000010476e000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
0: 44 24 10 rex.R and $0x10,%al
3: 4c 8b bc 24 20 02 00 mov 0x220(%rsp),%r15
a: 00
b: 83 7c 24 28 04 cmpl $0x4,0x28(%rsp)
10: 0f 85 aa 05 00 00 jne 0x5c0
16: 48 8b 9c 24 08 02 00 mov 0x208(%rsp),%rbx
1d: 00
1e: 48 89 d8 mov %rbx,%rax
21: 48 c1 e8 03 shr $0x3,%rax
25: 48 89 44 24 58 mov %rax,0x58(%rsp)
* 2a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 48 89 df mov %rbx,%rdi
34: e8 fa 2c c6 ff call 0xffc62d33
39: 4c 8b 23 mov (%rbx),%r12
3c: 4c 89 e6 mov %r12,%rsi
3f: 48 rex.W


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syz...@syzkaller.appspotmail.com

---
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