Re: [PATCH v5] locking/rwsem: Make handoff bit handling more consistent

[Waiman Long]

On 4/12/22 12:28, john.p.donnelly@xxxxxxxxxx wrote:
> On 4/11/22 4:07 PM, Waiman Long wrote:
> > On 4/11/22 17:03, john.p.donnelly@xxxxxxxxxx wrote:
> > > > > I have reached out to Waiman and he suggested this for our next 
> > > > > test pass:
> > > > >
> > > > >
> > > > > 1ee326196c6658 locking/rwsem: Always try to wake waiters in 
> > > > > out_nolock path
> > > >
> > > > Does this commit help to avoid the lockup problem?
> > > >
> > > > Commit 1ee326196c6658 fixes a potential missed wakeup problem when 
> > > > a reader first in the wait queue is interrupted out without 
> > > > acquiring the lock. It is actually not a fix for commit 
> > > > d257cc8cb8d5. However, this commit changes the out_nolock path 
> > > > behavior of writers by leaving the handoff bit set when the wait 
> > > > queue isn't empty. That likely makes the missed wakeup problem 
> > > > easier to reproduce.
> > > >
> > > > Cheers,
> > > > Longman
> > >
> > > Hi,
> > >
> > >
> > > We are testing now
> > >
> > > ETA for fio soak test completion is  ~15hr from now.
> > >
> > > I wanted to share the stack traces for future reference + occurrences.
> > I am looking forward to your testing results tomorrow.
> >
> > Cheers,
> > Longman
> Hi
>
>  Our 24hr fio soak test with :
>
>  1ee326196c6658 locking/rwsem: Always try to wake waiters in 
> out_nolock path
>
>
>  applied to 5.15.30  passed.
>
>  I suggest you append  1ee326196c6658 with :
>
>
>  cc: stable
>
>   Fixes: d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more 
> consistent")
>
>
> I'll leave the implementation details up to the core maintainers how 
> to do that ;-)

Thanks for the test.

The patch has already been in the tip tree. It may not be easy to add a 
Fixes tag to it. Anyway, I will encourage stable tree maintainer to take 
it as it does fix a problem as shown in your test.

Cheers,
Longman