[syzbot] [mm?] KCSAN: data-race in __delete_from_swap_cache / folio_mapping (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 39cd87c4eb2b Linux 6.9-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=129de21d180000
kernel config: https://syzkaller.appspot.com/x/.config?x=d024e89f7bb376ce
dashboard link: https://syzkaller.appspot.com/bug?extid=58fc2a881f3b3df5e336
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b9b2dcffd7d5/disk-39cd87c4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5f4981fa60e6/vmlinux-39cd87c4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/691f671f70ad/bzImage-39cd87c4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+58fc2a...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __delete_from_swap_cache / folio_mapping

write to 0xffffea0004798fa8 of 8 bytes by task 29 on cpu 0:
__delete_from_swap_cache+0x1f2/0x290 mm/swap_state.c:161
delete_from_swap_cache+0x72/0xe0 mm/swap_state.c:241
folio_free_swap+0x19f/0x1c0 mm/swapfile.c:1600
free_swap_cache mm/swap_state.c:290 [inline]
free_pages_and_swap_cache+0x1d9/0x400 mm/swap_state.c:322
__tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
tlb_flush_mmu+0x2cf/0x440 mm/mmu_gather.c:373
tlb_finish_mmu+0x8c/0x100 mm/mmu_gather.c:465
__oom_reap_task_mm+0x231/0x2e0 mm/oom_kill.c:553
oom_reap_task_mm mm/oom_kill.c:589 [inline]
oom_reap_task mm/oom_kill.c:613 [inline]
oom_reaper+0x264/0x850 mm/oom_kill.c:654
kthread+0x1d1/0x210 kernel/kthread.c:388
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

read to 0xffffea0004798fa8 of 8 bytes by task 14567 on cpu 1:
folio_mapping+0xd2/0x110 mm/util.c:797
folio_evictable mm/internal.h:256 [inline]
move_folios_to_lru+0x137/0x690 mm/vmscan.c:1808
shrink_inactive_list mm/vmscan.c:1929 [inline]
shrink_list mm/vmscan.c:2163 [inline]
shrink_lruvec+0xbd8/0x1640 mm/vmscan.c:5687
shrink_node_memcgs mm/vmscan.c:5873 [inline]
shrink_node+0xa78/0x15a0 mm/vmscan.c:5908
shrink_zones mm/vmscan.c:6152 [inline]
do_try_to_free_pages+0x3cc/0xca0 mm/vmscan.c:6214
try_to_free_mem_cgroup_pages+0x1eb/0x4e0 mm/vmscan.c:6529
try_charge_memcg+0x279/0xd10 mm/memcontrol.c:2783
try_charge mm/memcontrol.c:2931 [inline]
charge_memcg mm/memcontrol.c:7284 [inline]
mem_cgroup_swapin_charge_folio+0x107/0x1a0 mm/memcontrol.c:7369
__read_swap_cache_async+0x2b9/0x520 mm/swap_state.c:514
swap_cluster_readahead+0x276/0x3f0 mm/swap_state.c:678
swapin_readahead+0xe2/0x7a0 mm/swap_state.c:904
do_swap_page+0x3bb/0x15f0 mm/memory.c:4048
handle_pte_fault mm/memory.c:5303 [inline]
__handle_mm_fault mm/memory.c:5441 [inline]
handle_mm_fault+0x7fa/0x27e0 mm/memory.c:5606
do_user_addr_fault arch/x86/mm/fault.c:1413 [inline]
handle_page_fault arch/x86/mm/fault.c:1505 [inline]
exc_page_fault+0x2f5/0x6d0 arch/x86/mm/fault.c:1563
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
__get_user_8+0x11/0x20 arch/x86/lib/getuser.S:85
rseq_get_rseq_cs kernel/rseq.c:161 [inline]
rseq_ip_fixup kernel/rseq.c:281 [inline]
__rseq_handle_notify_resume+0xc8/0xc00 kernel/rseq.c:329
rseq_handle_notify_resume include/linux/rseq.h:38 [inline]
resume_user_mode_work include/linux/resume_user_mode.h:62 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x90/0x130 kernel/entry/common.c:218
do_syscall_64+0xe2/0x1d0 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x72/0x7a

value changed: 0x0000000000001198 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14567 Comm: syz-executor.1 Tainted: G W 6.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
==================================================================


---
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[Andrew Morton]

On Tue, 02 Apr 2024 13:10:29 -0700 syzbot <syzbot+58fc2a...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 39cd87c4eb2b Linux 6.9-rc2
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=129de21d180000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d024e89f7bb376ce
> dashboard link: https://syzkaller.appspot.com/bug?extid=58fc2a881f3b3df5e336
> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/b9b2dcffd7d5/disk-39cd87c4.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/5f4981fa60e6/vmlinux-39cd87c4.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/691f671f70ad/bzImage-39cd87c4.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+58fc2a...@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in __delete_from_swap_cache / folio_mapping
>
> write to 0xffffea0004798fa8 of 8 bytes by task 29 on cpu 0:
> __delete_from_swap_cache+0x1f2/0x290 mm/swap_state.c:161

folio->swap.val = 0;

> delete_from_swap_cache+0x72/0xe0 mm/swap_state.c:241
> folio_free_swap+0x19f/0x1c0 mm/swapfile.c:1600
> free_swap_cache mm/swap_state.c:290 [inline]
> free_pages_and_swap_cache+0x1d9/0x400 mm/swap_state.c:322
> __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
> tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
> tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
> tlb_flush_mmu+0x2cf/0x440 mm/mmu_gather.c:373
> tlb_finish_mmu+0x8c/0x100 mm/mmu_gather.c:465
> __oom_reap_task_mm+0x231/0x2e0 mm/oom_kill.c:553
> oom_reap_task_mm mm/oom_kill.c:589 [inline]
> oom_reap_task mm/oom_kill.c:613 [inline]
> oom_reaper+0x264/0x850 mm/oom_kill.c:654
> kthread+0x1d1/0x210 kernel/kthread.c:388
> ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
>
> read to 0xffffea0004798fa8 of 8 bytes by task 14567 on cpu 1:
> folio_mapping+0xd2/0x110 mm/util.c:797

return swap_address_space(folio->swap);

> folio_evictable mm/internal.h:256 [inline]
> move_folios_to_lru+0x137/0x690 mm/vmscan.c:1808
> shrink_inactive_list mm/vmscan.c:1929 [inline]
> shrink_list mm/vmscan.c:2163 [inline]
> shrink_lruvec+0xbd8/0x1640 mm/vmscan.c:5687
> shrink_node_memcgs mm/vmscan.c:5873 [inline]
> shrink_node+0xa78/0x15a0 mm/vmscan.c:5908
> shrink_zones mm/vmscan.c:6152 [inline]
> do_try_to_free_pages+0x3cc/0xca0 mm/vmscan.c:6214
>

> ...
>

These both point at David's 3d2c90876887 ("mm/swap: inline
folio_set_swap_entry() and folio_swap_entry()") which is probably
innocent, but I have to blame someone ;)

[David Hildenbrand]

On 03.04.24 23:44, Andrew Morton wrote:
> On Tue, 02 Apr 2024 13:10:29 -0700 syzbot <syzbot+58fc2a...@syzkaller.appspotmail.com> wrote:
>
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 39cd87c4eb2b Linux 6.9-rc2
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=129de21d180000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=d024e89f7bb376ce
>> dashboard link: https://syzkaller.appspot.com/bug?extid=58fc2a881f3b3df5e336
>> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>>
>> Unfortunately, I don't have any reproducer for this issue yet.
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/b9b2dcffd7d5/disk-39cd87c4.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/5f4981fa60e6/vmlinux-39cd87c4.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/691f671f70ad/bzImage-39cd87c4.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+58fc2a...@syzkaller.appspotmail.com
>>
>> ==================================================================
>> BUG: KCSAN: data-race in __delete_from_swap_cache / folio_mapping
>>
>> write to 0xffffea0004798fa8 of 8 bytes by task 29 on cpu 0:
>> __delete_from_swap_cache+0x1f2/0x290 mm/swap_state.c:161
>
> folio->swap.val = 0;

Here we are holding the folio lock and really must invalidate that swap
entry, because we are removing it from the swap cache.

>
>> delete_from_swap_cache+0x72/0xe0 mm/swap_state.c:241
>> folio_free_swap+0x19f/0x1c0 mm/swapfile.c:1600
>> free_swap_cache mm/swap_state.c:290 [inline]
>> free_pages_and_swap_cache+0x1d9/0x400 mm/swap_state.c:322
>> __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
>> tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
>> tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
>> tlb_flush_mmu+0x2cf/0x440 mm/mmu_gather.c:373
>> tlb_finish_mmu+0x8c/0x100 mm/mmu_gather.c:465
>> __oom_reap_task_mm+0x231/0x2e0 mm/oom_kill.c:553
>> oom_reap_task_mm mm/oom_kill.c:589 [inline]
>> oom_reap_task mm/oom_kill.c:613 [inline]
>> oom_reaper+0x264/0x850 mm/oom_kill.c:654
>> kthread+0x1d1/0x210 kernel/kthread.c:388
>> ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
>>
>> read to 0xffffea0004798fa8 of 8 bytes by task 14567 on cpu 1:
>> folio_mapping+0xd2/0x110 mm/util.c:797
>
> return swap_address_space(folio->swap);
>

And in this black-magic LRU thingy we don't.

We call folio_evictable()->folio_mapping()

Which ends up doing:

if (unlikely(folio_test_swapcache(folio))
return swap_address_space(folio->swap);

that can easily race with above code because we don't hold the folio lock.

Not sure if we should use READ_ONCE/WRITE_ONCE here, and try to handle
the race differently. We have to be prepared for
folio_test_swapcache()==true but then failing to get the address space
because we are concurrently removing the folio from the swapcache.

>> folio_evictable mm/internal.h:256 [inline]
>> move_folios_to_lru+0x137/0x690 mm/vmscan.c:1808
>> shrink_inactive_list mm/vmscan.c:1929 [inline]
>> shrink_list mm/vmscan.c:2163 [inline]
>> shrink_lruvec+0xbd8/0x1640 mm/vmscan.c:5687
>> shrink_node_memcgs mm/vmscan.c:5873 [inline]
>> shrink_node+0xa78/0x15a0 mm/vmscan.c:5908
>> shrink_zones mm/vmscan.c:6152 [inline]
>> do_try_to_free_pages+0x3cc/0xca0 mm/vmscan.c:6214
>>
>> ...
>>
>
> These both point at David's 3d2c90876887 ("mm/swap: inline
> folio_set_swap_entry() and folio_swap_entry()") which is probably
> innocent, but I have to blame someone ;)

Heh, I'm pretty sure that one is innocent. But also the other work in
the same series is likely innocent after staring at above race. But
nothing is impossible ;)

@Willy, Hugh, any idea regarding above race?

--
Cheers,

David / dhildenb