Re: KCSAN: data-race in taskstats_exit / taskstats_exit

[Dmitry Vyukov]

On Sat, Oct 5, 2019 at 6:26 AM syzbot
<syzbot+c5d03165a1bd1dead0c1@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    b4bd9343 x86, kcsan: Enable KCSAN for x86
> git tree:       https://github.com/google/ktsan.git kcsan
> console output: https://syzkaller.appspot.com/x/log.txt?x=125329db600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c0906aa620713d80
> dashboard link: https://syzkaller.appspot.com/bug?extid=c5d03165a1bd1dead0c1
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+c5d03165a1bd1dead0c1@xxxxxxxxxxxxxxxxxxxxxxxxx

+Christian, you wanted races in process mgmt ;)


> ==================================================================
> BUG: KCSAN: data-race in taskstats_exit / taskstats_exit
>
> write to 0xffff8881157bbe10 of 8 bytes by task 7951 on cpu 0:
>   taskstats_tgid_alloc kernel/taskstats.c:567 [inline]
>   taskstats_exit+0x6b7/0x717 kernel/taskstats.c:596
>   do_exit+0x2c2/0x18e0 kernel/exit.c:864
>   do_group_exit+0xb4/0x1c0 kernel/exit.c:983
>   get_signal+0x2a2/0x1320 kernel/signal.c:2734
>   do_signal+0x3b/0xc00 arch/x86/kernel/signal.c:815
>   exit_to_usermode_loop+0x250/0x2c0 arch/x86/entry/common.c:159
>   prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
>   do_syscall_64+0x2d7/0x2f0 arch/x86/entry/common.c:299
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> read to 0xffff8881157bbe10 of 8 bytes by task 7949 on cpu 1:
>   taskstats_tgid_alloc kernel/taskstats.c:559 [inline]
>   taskstats_exit+0xb2/0x717 kernel/taskstats.c:596
>   do_exit+0x2c2/0x18e0 kernel/exit.c:864
>   do_group_exit+0xb4/0x1c0 kernel/exit.c:983
>   __do_sys_exit_group kernel/exit.c:994 [inline]
>   __se_sys_exit_group kernel/exit.c:992 [inline]
>   __x64_sys_exit_group+0x2e/0x30 kernel/exit.c:992
>   do_syscall_64+0xcf/0x2f0 arch/x86/entry/common.c:296
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 7949 Comm: syz-executor.3 Not tainted 5.3.0+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> ==================================================================
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 7949 Comm: syz-executor.3 Not tainted 5.3.0+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0xf5/0x159 lib/dump_stack.c:113
>   panic+0x209/0x639 kernel/panic.c:219
>   end_report kernel/kcsan/report.c:135 [inline]
>   kcsan_report.cold+0x57/0xeb kernel/kcsan/report.c:283
>   __kcsan_setup_watchpoint+0x342/0x500 kernel/kcsan/core.c:456
>   __tsan_read8 kernel/kcsan/kcsan.c:31 [inline]
>   __tsan_read8+0x2c/0x30 kernel/kcsan/kcsan.c:31
>   taskstats_tgid_alloc kernel/taskstats.c:559 [inline]
>   taskstats_exit+0xb2/0x717 kernel/taskstats.c:596
>   do_exit+0x2c2/0x18e0 kernel/exit.c:864
>   do_group_exit+0xb4/0x1c0 kernel/exit.c:983
>   __do_sys_exit_group kernel/exit.c:994 [inline]
>   __se_sys_exit_group kernel/exit.c:992 [inline]
>   __x64_sys_exit_group+0x2e/0x30 kernel/exit.c:992
>   do_syscall_64+0xcf/0x2f0 arch/x86/entry/common.c:296
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x459a59
> Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffc4ccf3408 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 000000000000001e RCX: 0000000000459a59
> RDX: 0000000000413741 RSI: fffffffffffffff7 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 000000007f8e4506 R09: 00007ffc4ccf3460
> R10: ffffffff81007108 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ffc4ccf3460 R14: 0000000000000000 R15: 00007ffc4ccf3470
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
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