RE: [外部邮件] Re: [????] Re: [PATCH][RFC] hung_task: Support to panic when the maximum number of hung task warnings is reached

[Li,Rongqing]

> -----Original Message-----
> From: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Sent: 2025年9月23日 14:04
> To: Li,Rongqing <lirongqing@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; corbet@xxxxxxx;
> lance.yang@xxxxxxxxx; mhiramat@xxxxxxxxxx;
> pawan.kumar.gupta@xxxxxxxxxxxxxxx; mingo@xxxxxxxxxx;
> dave.hansen@xxxxxxxxxxxxxxx; rostedt@xxxxxxxxxxx; kees@xxxxxxxxxx;
> arnd@xxxxxxxx; feng.tang@xxxxxxxxxxxxxxxxx; pauld@xxxxxxxxxx;
> joel.granados@xxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: [外部邮件] Re: [????] Re: [PATCH][RFC] hung_task: Support to panic
> when the maximum number of hung task warnings is reached
> 
> On Tue, Sep 23, 2025 at 04:00:03AM +0000, Li,Rongqing wrote:
> >
> >
> > > -----Original Message-----
> > > From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > Sent: 2025年9月23日 11:46
> > > To: Li,Rongqing <lirongqing@xxxxxxxxx>
> > > Cc: corbet@xxxxxxx; lance.yang@xxxxxxxxx; mhiramat@xxxxxxxxxx;
> > > paulmck@xxxxxxxxxx; pawan.kumar.gupta@xxxxxxxxxxxxxxx;
> > > mingo@xxxxxxxxxx; dave.hansen@xxxxxxxxxxxxxxx; rostedt@xxxxxxxxxxx;
> > > kees@xxxxxxxxxx; arnd@xxxxxxxx; feng.tang@xxxxxxxxxxxxxxxxx;
> > > pauld@xxxxxxxxxx; joel.granados@xxxxxxxxxx;
> > > linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > Subject: [????] Re: [PATCH][RFC] hung_task: Support to panic when
> > > the maximum number of hung task warnings is reached
> > >
> > > On Tue, 23 Sep 2025 11:37:40 +0800 lirongqing <lirongqing@xxxxxxxxx>
> wrote:
> > >
> > > > Currently the hung task detector can either panic immediately or
> > > > continue operation when hung tasks are detected. However, there
> > > > are scenarios where we want a more balanced approach:
> > > >
> > > > - We don't want the system to panic immediately when a few hung tasks
> > > >   are detected, as the system may be able to recover
> > > > - And we also don't want the system to stall indefinitely with multiple
> > > >   hung tasks
> > > >
> > > > This commit introduces a new mode (value 2) for the hung task panic
> behavior.
> > > > When set to 2, the system will panic only after the maximum number
> > > > of hung task warnings (hung_task_warnings) has been reached.
> > > >
> > > > This provides a middle ground between immediate panic and
> > > > potentially infinite stall, allowing for automated vmcore
> > > > generation after a reasonable
> > >
> > > I assume the same argument applies to the NMI watchdog, to the
> > > softlockup detector and to the RCU stall detector?
> >
> > True, especial RCU stall detector
> 
> There are the panic_on_rcu_stall and max_rcu_stall_to_panic sysctls, which
> together allow you to panic after (say) three RCU CPU stall warnings.
> Does those do what you need?



Yes, this is what I need. RCU has been implemented.

Thanks


-Li

> 
> 							Thanx, Paul
> 
> > > A general framework to handle all of these might be better.  But why
> > > do it in kernel at all?  What about a userspace detector which
> > > parses kernel logs (or new procfs counters) and makes such decisions?
> >
> >
> > By leveraging existing kernel mechanisms, implementation in kernel is
> > very simple and reliable, I think
> >
> > Thanks
> >
> > -Li
> >