linux-kernel - Re: [syzbot] [kernel?] WARNING: suspicious RCU usage in __do

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Date: Fri, 26 Apr 2024 10:09:39 +0800
From: Z qiang <qiang.zhang1211@...il.com>
To: paulmck@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, 
	syzbot <syzbot+dce04ed6d1438ad69656@...kaller.appspotmail.com>, 
	linux-kernel@...r.kernel.org, peterz@...radead.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] WARNING: suspicious RCU usage in __do_softirq

>
> On Tue, Apr 23, 2024 at 10:20:49AM +0800, Z qiang wrote:
> > >
> > > On Fri, Apr 19 2024 at 13:50, Z qiang wrote:
> > > >> On Thu, Apr 18, 2024 at 05:49:38PM +0800, Z qiang wrote:
> > > >  static __init int spawn_ksoftirqd(void)
> > > >  {
> > > > +       int cpu;
> > > > +
> > > > +       for_each_possible_cpu(cpu)
> > > > +               per_cpu(ksoftirqd_work, cpu) = false;
> > >
> > > First of all that initialization is pointless, but why making all of
> > > this complex as hell?
> > >
> > > Thanks,
> > >
> > >         tglx
> > > ---
> > > diff --git a/kernel/softirq.c b/kernel/softirq.c
> > > index b315b21fb28c..e991d735be0d 100644
> > > --- a/kernel/softirq.c
> > > +++ b/kernel/softirq.c
> > > @@ -508,7 +508,7 @@ static inline bool lockdep_softirq_start(void) { return false; }
> > >  static inline void lockdep_softirq_end(bool in_hardirq) { }
> > >  #endif
> > >
> > > -asmlinkage __visible void __softirq_entry __do_softirq(void)
> > > +static void handle_softirqs(bool kirqd)
> > >  {
> > >         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
> > >         unsigned long old_flags = current->flags;
> > > @@ -563,8 +563,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
> > >                 pending >>= softirq_bit;
> > >         }
> > >
> > > -       if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
> > > -           __this_cpu_read(ksoftirqd) == current)
> > > +       if (!IS_ENABLED(CONFIG_PREEMPT_RT) && kirqd)
> > >                 rcu_softirq_qs();
> > >
> > >         local_irq_disable();
> > > @@ -584,6 +583,11 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
> > >         current_restore_flags(old_flags, PF_MEMALLOC);
> > >  }
> > >
> > > +asmlinkage __visible void __softirq_entry __do_softirq(void)
> > > +{
> > > +       handle_softirqs(false);
> > > +}
> > > +
> > >  /**
> > >   * irq_enter_rcu - Enter an interrupt context with RCU watching
> > >   */
> > > @@ -921,7 +925,7 @@ static void run_ksoftirqd(unsigned int cpu)
> > >                  * We can safely run softirq on inline stack, as we are not deep
> > >                  * in the task stack here.
> > >                  */
> > > -               __do_softirq();
> > > +               handle_softirqs(true);
> >
> > Thanks, this is good for me :),
> > Paul, what do you think?
>
> This looks quite nice to me, especially given that it avoids changing
> all the other calls to __do_softirq().  Some architectures might want
> to directly call handle_softirqs(), but if so, they can send the patches.


Hello, Thomas
Can you send an official patch? or I will send and add you to
Co-developed-by tags.

Thanks
Zqiang


>
>                                                         Thanx, Paul
>
> > Thanks
> > Zqiang
> >
> > >                 ksoftirqd_run_end();
> > >                 cond_resched();
> > >                 return;