> On Mon, Oct 14, 2024 at 7:00 PM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > 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 > > > > > I tried to reproduce it but i am not able to. For the other hand, it is obvious that a reading "krcp->monitor_work.timer.expires" and simultaneous writing is possible. So, we can address it, i mean to prevent such parallel access by following patch: <snip> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e641cc681901..d711870fde84 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3531,7 +3531,7 @@ static int krc_count(struct kfree_rcu_cpu *krcp) } static void -schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) +__schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) { long delay, delay_left; @@ -3545,6 +3545,16 @@ schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) queue_delayed_work(system_wq, &krcp->monitor_work, delay); } +static void +schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&krcp->lock, flags); + __schedule_delayed_monitor_work(krcp); + raw_spin_unlock_irqrestore(&krcp->lock, flags); +} + static void kvfree_rcu_drain_ready(struct kfree_rcu_cpu *krcp) { @@ -3841,7 +3851,7 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr) // Set timer to drain after KFREE_DRAIN_JIFFIES. if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING) - schedule_delayed_monitor_work(krcp); + __schedule_delayed_monitor_work(krcp); unlock_return: krc_this_cpu_unlock(krcp, flags); <snip> i will send out the patch after some testing! -- Uladzislau Rezki
