[moderation] [fs?] KASAN: null-ptr-deref Read in drop_buffers (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8d561baae505 Merge tag 'x86_urgent_for_v6.17_rc2' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ae6ba2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ce98061fb8ee27bc
dashboard link: https://syzkaller.appspot.com/bug?extid=442c982d16f70806ac9b
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f389f23fc1cf/disk-8d561baa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/80cec102f6f0/vmlinux-8d561baa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8891bce062b1/bzImage-8d561baa.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+442c98...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: null-ptr-deref in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
BUG: KASAN: null-ptr-deref in buffer_busy fs/buffer.c:2886 [inline]
BUG: KASAN: null-ptr-deref in drop_buffers+0x65/0x4f0 fs/buffer.c:2898
Read of size 4 at addr 0000000000000060 by task syz.9.10589/3505

CPU: 0 UID: 0 PID: 3505 Comm: syz.9.10589 Not tainted 6.17.0-rc1-syzkaller-00224-g8d561baae505 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
kasan_report+0x118/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:189
instrument_atomic_read include/linux/instrumented.h:68 [inline]
atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
buffer_busy fs/buffer.c:2886 [inline]
drop_buffers+0x65/0x4f0 fs/buffer.c:2898
try_to_free_buffers+0x1e1/0x2d0 fs/buffer.c:2952
shrink_folio_list+0x20ac/0x4cd0 mm/vmscan.c:1518
evict_folios+0x47f2/0x58b0 mm/vmscan.c:4744
try_to_shrink_lruvec+0x8a3/0xb50 mm/vmscan.c:4907
shrink_one+0x21b/0x7c0 mm/vmscan.c:4952
shrink_many mm/vmscan.c:5015 [inline]
lru_gen_shrink_node mm/vmscan.c:5093 [inline]
shrink_node+0x314e/0x3760 mm/vmscan.c:6078
shrink_zones mm/vmscan.c:6336 [inline]
do_try_to_free_pages+0x668/0x1960 mm/vmscan.c:6398
try_to_free_pages+0x8a2/0xdd0 mm/vmscan.c:6644
__perform_reclaim mm/page_alloc.c:4310 [inline]
__alloc_pages_direct_reclaim+0x144/0x300 mm/page_alloc.c:4332
__alloc_pages_slowpath+0x5ff/0xce0 mm/page_alloc.c:4781
__alloc_frozen_pages_noprof+0x319/0x370 mm/page_alloc.c:5161
__alloc_pages_noprof mm/page_alloc.c:5182 [inline]
__folio_alloc_noprof+0x18/0x120 mm/page_alloc.c:5192
alloc_charge_folio+0x3c7/0x830 mm/khugepaged.c:1088
collapse_file mm/khugepaged.c:1863 [inline]
hpage_collapse_scan_file+0x17cf/0x4fa0 mm/khugepaged.c:2377
madvise_collapse+0x45b/0xa40 mm/khugepaged.c:2809
madvise_vma_behavior+0xec8/0x3af0 mm/madvise.c:1358
madvise_walk_vmas+0x51c/0xa30 mm/madvise.c:1669
madvise_do_behavior+0x38e/0x550 mm/madvise.c:1885
do_madvise+0x1bc/0x270 mm/madvise.c:1978
__do_sys_madvise mm/madvise.c:1987 [inline]
__se_sys_madvise mm/madvise.c:1985 [inline]
__x64_sys_madvise+0xa7/0xc0 mm/madvise.c:1985
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f93f7f8ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f93f8e6f038 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f93f81b6090 RCX: 00007f93f7f8ebe9
RDX: 0000000000000019 RSI: 0000000000600003 RDI: 0000200000000000
RBP: 00007f93f8011e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f93f81b6128 R14: 00007f93f81b6090 R15: 00007ffc3a264aa8
</TASK>
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.