All of lore.kernel.org
 help / color / mirror / Atom feed
From: Wu Fengguang <wfg@linux.intel.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Илья Тумайкин" <librarian_rus@yahoo.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org
Subject: Re: A regression in recent 3.2 kernel: bdi_dirty_limit() divide error
Date: Sun, 8 Jan 2012 10:33:05 +0800	[thread overview]
Message-ID: <20120108023305.GA5074@localhost> (raw)
In-Reply-To: <1325954125.2442.27.camel@twins>

On Sat, Jan 07, 2012 at 05:35:25PM +0100, Peter Zijlstra wrote:
> On Sat, 2012-01-07 at 22:56 +0800, Wu Fengguang wrote:
> > Subject: 
> > Date: Sat Jan 07 22:50:45 CST 2012
> > 
> > The uninitilized shift may lead to denominator=0 in
> > prop_fraction_percpu() and divide error in bdi_dirty_limit().
> 
> I'm not seeing how, only proc_change_shift() can change ->index, and it
> does that after it writes ->pg[index]->shift.

Then I lose the clue why bdi_dirty_limit() will divide error at all.

prop_change_shift() does

        change ->pg[index]->shift
        smp_wmb()
        change ->index

Will the read side prop_fraction_percpu() need some read memory barrier?

Thanks,
Fengguang

  reply	other threads:[~2012-01-08  2:33 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1325884395.57034.YahooMailClassic@web161605.mail.bf1.yahoo.com>
2012-01-07 14:56 ` A regression in recent 3.2 kernel: bdi_dirty_limit() divide error Wu Fengguang
2012-01-07 16:35   ` Peter Zijlstra
2012-01-08  2:33     ` Wu Fengguang [this message]
2012-01-08 10:19       ` Peter Zijlstra
2012-01-09  4:04         ` Wu Fengguang
     [not found]           ` <1326205945.62365.YahooMailClassic@web161603.mail.bf1.yahoo.com>
2012-01-10 14:38             ` Wu Fengguang
2012-01-10 14:38               ` Wu Fengguang
2012-01-09  4:55         ` Wu Fengguang
2012-01-10 14:54           ` [PATCH] lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel Wu Fengguang
2012-01-10 15:01             ` Wu Fengguang

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20120108023305.GA5074@localhost \
    --to=wfg@linux.intel.com \
    --cc=a.p.zijlstra@chello.nl \
    --cc=librarian_rus@yahoo.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.