linux-kernel - Re: There is a Tasks RCU stall warning

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 12 Apr 2017 10:59:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: There is a Tasks RCU stall warning

On Wed, 12 Apr 2017 07:48:00 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> > > > Like this?  (Untested, but builds at least some of the time.)  
> > > 
> > > Not like that...  :-/  Update on its way.  
> > 
> > Perhaps more like this.  Started rcutorture on it, will see how it goes.  

I just love the above discussion with yourself ;-)

> 
> Do you need this patch?  If so, I should do some more work on it to
> eliminate the extra common-case branch on the scheduler fastpath.
> 

Do I still need this patch? Maybe. :-)

I changed my benchmark test to call cond_resched_rcu_qs() instead and
that appears to fix the issue. But I'm not sure if there's any other
kthread out there that just calls cond_resched() or schedule().

Actually, I think it is still a good idea to have it. I believe that it
will still allow synchronize_rcu_tasks() to progress even if there's a
kthread task that is constantly being woken up, and never sleeps when
it calls schedule(), as it may always have the R state.

-- Steve