linux-kernel - Re: [RCU] rcu_tasks_trace_qs(): trc_reader_special.b.need

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]

Message-ID: <20231205155927.4b3b9151@gandalf.local.home>
Date:   Tue, 5 Dec 2023 15:59:27 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, rcu@...r.kernel.org,
        Frederic Weisbecker <fweisbec@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [RCU] rcu_tasks_trace_qs(): trc_reader_special.b.need_qs value
 incorrect likely()?

On Sat, 2 Dec 2023 18:45:07 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sat, 2 Dec 2023 14:24:26 -0800
> "Paul E. McKenney" <paulmck@...nel.org> wrote:
> 
> > > Note, the unlikely tracing is running on my production server v6.6.3.
> > > 
> > > The above trace is from my test box with latest Linus's tree.    
> > 
> > Nice tool!!!  
> 
> Thanks! It's only been in the kernel since 2008 ;-)
> 
>   1f0d69a9fc815 ("tracing: profile likely and unlikely annotations")
> 
> > 
> > My kneejerk reaction is that that condition is suboptimal.  Does the 
> > (untested) patch below help things?  
> 
> I'll give it a try on Monday.
> 

This looks to have caused a difference. Although there's other RCU
functions that need dealing with, but that's for when I have time to
analyze all the places that have bad annotations.


Anyway:

 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
 [..]
   17924        0   0 rcu_softirq_qs                 tree.c               247

Tested-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve