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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Tue, 25 Apr 2023 08:08:24 -0700
Message-ID: <CAADnVQK3m34RPCgw-7qWxE4gBb+ZoX4ZmEtbe-Ku0_ZOSG+5vA@mail.gmail.com>
Subject: Re: [syzbot] [bpf?] KCSAN: data-race in __bpf_lru_list_rotate /
 __htab_lru_percpu_map_update_elem (5)
To:     syzbot <syzbot+ebe648a84e8784763f82@syzkaller.appspotmail.com>,
        Martin KaFai Lau <martin.lau@kernel.org>
Cc:     andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, haoluo@google.com, john.fastabend@gmail.com,
        jolsa@kernel.org, kpsingh@kernel.org, linux-kernel@vger.kernel.org,
        martin.lau@linux.dev, sdf@google.com, song@kernel.org,
        syzkaller-bugs@googlegroups.com, yhs@fb.com
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Martin,


Please take a look at the trace below.
I think we just need to annotate bpf_lru_node_set_ref() with data_race().
wdyt?

Too bad there is no reproducer.

On Tue, Apr 25, 2023 at 12:31=E2=80=AFAM syzbot
<syzbot+ebe648a84e8784763f82@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    6a66fdd29ea1 Merge tag 'rust-fixes-6.3' of https://github=
...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=3D160d894828000=
0
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3Dfa4baf7c6b35b=
5d5
> dashboard link: https://syzkaller.appspot.com/bug?extid=3Debe648a84e87847=
63f82
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Deb=
ian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/78937867b23a/dis=
k-6a66fdd2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/dfd6c176adff/vmlinu=
x-6a66fdd2.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/51509bf47166/b=
zImage-6a66fdd2.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the comm=
it:
> Reported-by: syzbot+ebe648a84e8784763f82@syzkaller.appspotmail.com
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> BUG: KCSAN: data-race in __bpf_lru_list_rotate / __htab_lru_percpu_map_up=
date_elem
>
> write to 0xffff888137038deb of 1 bytes by task 11240 on cpu 1:
>  __bpf_lru_node_move kernel/bpf/bpf_lru_list.c:113 [inline]
>  __bpf_lru_list_rotate_active kernel/bpf/bpf_lru_list.c:149 [inline]
>  __bpf_lru_list_rotate+0x1bf/0x750 kernel/bpf/bpf_lru_list.c:240
>  bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:329 [inline]
>  bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
>  bpf_lru_pop_free+0x638/0xe20 kernel/bpf/bpf_lru_list.c:499
>  prealloc_lru_pop kernel/bpf/hashtab.c:290 [inline]
>  __htab_lru_percpu_map_update_elem+0xe7/0x820 kernel/bpf/hashtab.c:1316
>  bpf_percpu_hash_update+0x5e/0x90 kernel/bpf/hashtab.c:2313
>  bpf_map_update_value+0x2a9/0x370 kernel/bpf/syscall.c:200
>  generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1687
>  bpf_map_do_batch+0x2d9/0x3d0 kernel/bpf/syscall.c:4534
>  __sys_bpf+0x338/0x810
>  __do_sys_bpf kernel/bpf/syscall.c:5096 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5094 [inline]
>  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5094
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> read to 0xffff888137038deb of 1 bytes by task 11241 on cpu 0:
>  bpf_lru_node_set_ref kernel/bpf/bpf_lru_list.h:70 [inline]
>  __htab_lru_percpu_map_update_elem+0x2f1/0x820 kernel/bpf/hashtab.c:1332
>  bpf_percpu_hash_update+0x5e/0x90 kernel/bpf/hashtab.c:2313
>  bpf_map_update_value+0x2a9/0x370 kernel/bpf/syscall.c:200
>  generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1687
>  bpf_map_do_batch+0x2d9/0x3d0 kernel/bpf/syscall.c:4534
>  __sys_bpf+0x338/0x810
>  __do_sys_bpf kernel/bpf/syscall.c:5096 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5094 [inline]
>  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5094
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> value changed: 0x01 -> 0x00
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 11241 Comm: syz-executor.3 Not tainted 6.3.0-rc7-syzkaller-00=
136-g6a66fdd29ea1 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS G=
oogle 03/30/2023
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.