Re: [syzbot] [bpf?] KCSAN: data-race in __mod_timer / kvfree_call_rcu

[Dmitry Vyukov]

On Mon, 14 Oct 2024 at 08:07, syzbot
<syzbot+061d370693bdd99f9d34@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    5b7c893ed5ed Merge tag 'ntfs3_for_6.12' of https://github...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=148ae327980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a2f7ae2f221e9eae
> dashboard link: https://syzkaller.appspot.com/bug?extid=061d370693bdd99f9d34
> 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/79bb9e82835a/disk-5b7c893e.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/5931997fd31c/vmlinux-5b7c893e.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/fc8cc3d97b18/bzImage-5b7c893e.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+061d370693bdd99f9d34@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KCSAN: data-race in __mod_timer / kvfree_call_rcu
>
> read to 0xffff888237d1cce8 of 8 bytes by task 10149 on cpu 1:
>  schedule_delayed_monitor_work kernel/rcu/tree.c:3520 [inline]

+rcu maintainers, this looks more like rcu issue

#syz set subsystems: rcu

>  kvfree_call_rcu+0x3b8/0x510 kernel/rcu/tree.c:3839
>  trie_update_elem+0x47c/0x620 kernel/bpf/lpm_trie.c:441
>  bpf_map_update_value+0x324/0x350 kernel/bpf/syscall.c:203
>  generic_map_update_batch+0x401/0x520 kernel/bpf/syscall.c:1849
>  bpf_map_do_batch+0x28c/0x3f0 kernel/bpf/syscall.c:5143
>  __sys_bpf+0x2e5/0x7a0
>  __do_sys_bpf kernel/bpf/syscall.c:5741 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5739 [inline]
>  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5739
>  x64_sys_call+0x2625/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:322
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> write to 0xffff888237d1cce8 of 8 bytes by task 56 on cpu 0:
>  __mod_timer+0x578/0x7f0 kernel/time/timer.c:1173
>  add_timer_global+0x51/0x70 kernel/time/timer.c:1330
>  __queue_delayed_work+0x127/0x1a0 kernel/workqueue.c:2523
>  queue_delayed_work_on+0xdf/0x190 kernel/workqueue.c:2552
>  queue_delayed_work include/linux/workqueue.h:677 [inline]
>  schedule_delayed_monitor_work kernel/rcu/tree.c:3525 [inline]
>  kfree_rcu_monitor+0x5e8/0x660 kernel/rcu/tree.c:3643
>  process_one_work kernel/workqueue.c:3229 [inline]
>  process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
>  worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
>  kthread+0x1d1/0x210 kernel/kthread.c:389
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 UID: 0 PID: 56 Comm: kworker/u8:4 Not tainted 6.12.0-rc2-syzkaller-00050-g5b7c893ed5ed #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Workqueue: events_unbound kfree_rcu_monitor
> ==================================================================
> bridge0: port 2(bridge_slave_1) entered blocking state
> bridge0: port 2(bridge_slave_1) entered forwarding state
>
>
> ---
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