Re: KCSAN: data-race in binder_dec_node_nilocked / binder_state_show

[Todd Kjos]

+Hridya Valsaraju

On Fri, Apr 3, 2020 at 5:35 AM syzbot
<syzbot+71f39766a98dddab97b5@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    245a4300 Merge branch 'rcu/kcsan' into tip/locking/kcsan
> git tree:       https://github.com/google/ktsan.git kcsan
> console output: https://syzkaller.appspot.com/x/log.txt?x=106b67f1e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a4b9db179318d21f
> dashboard link: https://syzkaller.appspot.com/bug?extid=71f39766a98dddab97b5
> 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+71f39766a98dddab97b5@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KCSAN: data-race in binder_dec_node_nilocked / binder_state_show
>
> write to 0xffff88809f276954 of 4 bytes by task 1408 on cpu 0:
>  binder_state_show+0xd8/0x260 drivers/android/binder.c:5938
>  seq_read+0x350/0x9d0 fs/seq_file.c:229
>  full_proxy_read+0xbd/0x100 fs/debugfs/file.c:220
>  do_loop_readv_writev fs/read_write.c:714 [inline]
>  do_loop_readv_writev fs/read_write.c:701 [inline]
>  do_iter_read+0x357/0x3d0 fs/read_write.c:935
>  vfs_readv+0x9c/0xf0 fs/read_write.c:997
>  do_preadv+0x131/0x1d0 fs/read_write.c:1089
>  __do_sys_preadv fs/read_write.c:1139 [inline]
>  __se_sys_preadv fs/read_write.c:1134 [inline]
>  __x64_sys_preadv+0x61/0x80 fs/read_write.c:1134
>  do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> read to 0xffff88809f276954 of 4 bytes by task 1416 on cpu 1:
>  binder_dec_node_nilocked+0x382/0x610 drivers/android/binder.c:1261
>  binder_dec_node_tmpref+0xa3/0x120 drivers/android/binder.c:1379
>  binder_put_node drivers/android/binder.c:1387 [inline]
>  binder_state_show+0x1aa/0x260 drivers/android/binder.c:5950
>  seq_read+0x350/0x9d0 fs/seq_file.c:229
>  full_proxy_read+0xbd/0x100 fs/debugfs/file.c:220
>  do_loop_readv_writev fs/read_write.c:714 [inline]
>  do_loop_readv_writev fs/read_write.c:701 [inline]
>  do_iter_read+0x357/0x3d0 fs/read_write.c:935
>  vfs_readv+0x9c/0xf0 fs/read_write.c:997
>  do_preadv+0x131/0x1d0 fs/read_write.c:1089
>  __do_sys_preadv fs/read_write.c:1139 [inline]
>  __se_sys_preadv fs/read_write.c:1134 [inline]
>  __x64_sys_preadv+0x61/0x80 fs/read_write.c:1134
>  do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 1416 Comm: syz-executor.1 Not tainted 5.5.0-rc1-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> ==================================================================
>
>
> ---
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>
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