KCSAN: data-race in binder_dec_node_nilocked / binder_state_show

[syzbot]

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 at syzkaller.appspotmail.com

==================================================================
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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