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

[Paul E. McKenney]

On Mon, Oct 14, 2024 at 10:27:05AM +0200, Dmitry Vyukov wrote:
> 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]

This is the access to krcp->monitor_work.timer.expires in the function
schedule_delayed_monitor_work().

Uladzislau, could you please take a look at this one?

							Thanx, Paul

> +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
> >
> >
> > ---
> > 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@xxxxxxxxxxxxxxxx.
> >
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> >
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> >
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