On Tue, Feb 25, 2025 at 08:11:11AM -0800, Boqun Feng wrote:
> On Tue, Feb 25, 2025 at 08:08:53AM -0800, Boqun Feng wrote:
> > On Tue, Feb 25, 2025 at 07:58:01AM -0800, Paul E. McKenney wrote:
> > > Hello, Boqun,
> > >
> > > I have run overnight tests on your earlier branches here:
> > >
> > > ccb986e8b69f ("MAINTAINERS: Update Joel's email address")
> > >
>
> Oh and I should have let you know, I updated next and dev branch, the
> latest ones are:
>
> next.2025.02.24a and dev.2025.02.24a in rcu repo.
Very well, I will try them out later today.
> Regards,
> Boqun
>
> > > These passed other than a KCSAN complaint involving
> > > rcu_preempt_deferred_qs_handler() and rcu_read_unlock_special().
> > > This looks like the plain C-language writes to ->defer_qs_iw_pending.
> > >
> > > My guess is that this is low probability, despite having happened twice,
> > > and that it happens when rcu_read_unlock_special() is interrupted,
> > > resulting in rcu_preempt_deferred_qs_handler() being invoked as an
> > > IRQ-work handler. Keeping in mind that RCU runs KCSAN so as to locate
> > > data races between task and handler on the same CPU.
> > >
> > > Thoughts?
> > >
> >
> > Do you have a KCSAN of this? Also this is not a regression, right?
> > Meaning you probably have seen this before? Anyway, it should be an easy
> > fix (just using READ_ONCE() and WRITE_ONCE()). I can send the fix out
> > and put it in.
Here you go! And you are right, if it is a regression, it is from a
long time ago, though something more recent might have made it more
probable.
In any case, not at all urgent.
Thanx, Paul
------------------------------------------------------------------------
[ 624.037869] ==================================================================
[ 624.037883] BUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special
[ 624.037906]
[ 624.037909] read to 0xffffa034df2eff90 of 1 bytes by task 45 on cpu 3:
[ 624.037916] rcu_read_unlock_special+0x177/0x260
[ 624.037925] __rcu_read_unlock+0x92/0xa0
[ 624.037935] rt_spin_unlock+0x9b/0xc0
[ 624.037946] __local_bh_enable+0x10e/0x170
[ 624.037957] __local_bh_enable_ip+0xe9/0x140
[ 624.037967] rcu_cpu_kthread+0x95f/0x1190
[ 624.037976] smpboot_thread_fn+0x230/0x320
[ 624.037985] kthread+0x3b8/0x400
[ 624.037995] ret_from_fork+0x35/0x40
[ 624.038025] ret_from_fork_asm+0x1a/0x30
[ 624.038036]
[ 624.038039] write to 0xffffa034df2eff90 of 1 bytes by task 43 on cpu 3:
[ 624.038046] rcu_preempt_deferred_qs_handler+0x1e/0x30
[ 624.038057] irq_work_single+0xaf/0x160
[ 624.038066] run_irq_workd+0x92/0xd0
[ 624.038075] smpboot_thread_fn+0x230/0x320
[ 624.038085] kthread+0x3b8/0x400
[ 624.038095] ret_from_fork+0x35/0x40
[ 624.038105] ret_from_fork_asm+0x1a/0x30
[ 624.038116]
[ 624.038118] no locks held by irq_work/3/43.
[ 624.038123] irq event stamp: 202724
[ 624.038126] hardirqs last enabled at (202724): [<ffffffffa8950831>] finish_task_switch+0x131/0x320
[ 624.038138] hardirqs last disabled at (202723): [<ffffffffa9f8ce02>] __schedule+0xe2/0xbb0
[ 624.038146] softirqs last enabled at (0): [<ffffffffa88dbfd1>] copy_process+0x4e1/0x1cc0
[ 624.038159] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 624.038167]
[ 624.038169] Reported by Kernel Concurrency Sanitizer on:
[ 624.038173] CPU: 3 UID: 0 PID: 43 Comm: irq_work/3 Not tainted 6.14.0-rc1-00080-gd6558730a4de #6410
[ 624.038185] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 624.038191] ==================================================================
