linux-kernel - Re: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies.

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:   Fri, 05 May 2017 01:33:29 -0500
From:   Scott Wood <oss@...error.net>
To:     Karim Eshapa <karim.eshapa@...il.com>
Cc:     claudiu.manoil@....com, roy.pledge@....com,
        colin.king@...onical.com, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck
 hacking jiffies.

On Fri, 2017-05-05 at 08:01 +0200, Karim Eshapa wrote:
> > On 5/4/2017 5:07 PM, Scott Wood wrote:
> > > On Thu, 2017-05-04 at 06:58 +0200, Karim Eshapa wrote:
> > > > +    stop = jiffies + 10000;
> > > > +    /*
> > > > +     * if MR was full and h/w had other FQRNI entries to produce, we
> > > > +     * need to allow it time to produce those entries once the
> > > > +     * existing entries are consumed. A worst-case situation
> > > > +     * (fully-loaded system) means h/w sequencers may have to do 3-4
> > > > +     * other things before servicing the portal's MR pump, each of
> > > > +     * which (if slow) may take ~50 qman cycles (which is ~200
> > > > +     * processor cycles). So rounding up and then multiplying this
> > > > +     * worst-case estimate by a factor of 10, just to be
> > > > +     * ultra-paranoid, goes as high as 10,000 cycles. NB, we consume
> > > > +     * one entry at a time, so h/w has an opportunity to produce new
> > > > +     * entries well before the ring has been fully consumed, so
> > > > +     * we're being *really* paranoid here.
> > > > +     */
> > > 
> > > OK, upon reading this more closely it seems the intent was to delay for
> > > 10,000
> > > *processor cycles* and somehow that got turned into 10,000 jiffies
> > > (which is
> > > 40 seconds at the default Hz!).  We could just replace this whole thing
> > > with
> > > msleep(1) and still be far more paranoid than was originally intended.
> > > 
> > > Claudiu and Roy, any comments?
> > 
> > Yes the timing here is certainly off, the code changed a few times since
> > the comment was originally written.
> > An msleep(1) seems reasonable here to me.
> 
> If the previous patch with msleep(1) is OK.
> can I send a patch to slightly change the comments.

Yes.

-Scott