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Date: Wed, 3 Apr 2024 14:44:52 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: syzbot <syzbot+58fc2a881f3b3df5e336@syzkaller.appspotmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 syzkaller-bugs@googlegroups.com, David Hildenbrand <david@redhat.com>
Subject: Re: [syzbot] [mm?] KCSAN: data-race in __delete_from_swap_cache /
 folio_mapping (3)
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On Tue, 02 Apr 2024 13:10:29 -0700 syzbot <syzbot+58fc2a881f3b3df5e336@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+58fc2a881f3b3df5e336@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 ;)