linux-kernel - Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree

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] [day] [month] [year] [list]

Message-Id: <20190814165927.GT28441@linux.ibm.com>
Date:   Wed, 14 Aug 2019 09:59:27 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Byungchul Park <byungchul.park@....com>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Byungchul Park <max.byungchul.park@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Rao Shoaib <rao.shoaib@...cle.com>, kernel-team@...roid.com,
        kernel-team <kernel-team@....com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu <rcu@...r.kernel.org>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu
 batching

On Wed, Aug 14, 2019 at 12:43:10PM +0900, Byungchul Park wrote:
> On Tue, Aug 13, 2019 at 07:53:49PM -0700, Paul E. McKenney wrote:
> > On Wed, Aug 14, 2019 at 09:11:03AM +0900, Byungchul Park wrote:
> > > On Tue, Aug 13, 2019 at 08:41:45AM -0700, Paul E. McKenney wrote:
> > > > On Tue, Aug 13, 2019 at 02:29:54PM +0900, Byungchul Park wrote:
> > > > > On Mon, Aug 12, 2019 at 09:12:34AM -0400, Joel Fernandes wrote:
> > > > > > On Mon, Aug 12, 2019 at 07:10:52PM +0900, Byungchul Park wrote:
> > > > > > > On Sun, Aug 11, 2019 at 04:49:39PM -0700, Paul E. McKenney wrote:
> > > > > > > > Maybe.  Note well that I said "potential issue".  When I checked a few
> > > > > > > > years ago, none of the uses of rcu_barrier() cared about kfree_rcu().
> > > > > > > > They cared instead about call_rcu() callbacks that accessed code or data
> > > > > > > > that was going to disappear soon, for example, due to module unload or
> > > > > > > > filesystem unmount.
> > > > > > > > 
> > > > > > > > So it -might- be that rcu_barrier() can stay as it is, but with changes
> > > > > > > > as needed to documentation.
> > > > > > 
> > > > > > Right, we should update the docs. Byungchul, do you mind sending a patch that
> > > > > > documents the rcu_barrier() behavior?
> > > > > 
> > > > > Are you trying to give me the chance? I feel thankful. It doens't matter
> > > > > to try it at the moment though, I can't follow-up until September. I'd
> > > > > better do that in Septamber or give it up this time.
> > > > 
> > > > Which reminds me...  I recall your asking if the kfree_rcu() patch
> > > > might be sensitive to the exact hardware, but I cannot locate that
> > > > email right off-hand.  This is an excellent question!  When faced with
> > > > floods of kfree_rcu() calls, I would expect some hardware, compiler,
> > > > and kernel-configuration sensitivity.  Which is why it will likely be
> > > 
> > > Yes.
> > > 
> > > > necessary to do a few more improvements over time -- for but one example,
> > > > accumulating callbacks into vectors in order to reduce the number of
> > > > kfree()-time cache misses.
> > > 
> > > Yes. That would be a pretty good way to mitigate the problem. I hope
> > > the simple way we've done works well enough so it would never happen
> > > though.
> > > 
> > > Or I would check the condition of all system resourses e.g. CPU and
> > > memory and control the bandwith of them, of course only if that actually
> > > happens.
> > > 
> > > Thanks a lot for sharing your opinion on it!
> > 
> > Didn't you say earlier that you were getting OOM on your system even
> > with the patches?  Or did I miss the resolution of that issue?
> 
> I said I saw OOM with a *larger* value of KFREE_DRAIN_JIFFIES. It was
> fine with the patch itself.

Got it, thank you!

> Anyway I'm sorry I expressed it in a confusing way.

But what is life without a little confusion?  ;-)

							Thanx, Paul