LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Jarek Poplawski <jarkao2@o2.pl>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	David Howells <dhowells@redhat.com>,
	David Miller <davem@davemloft.net>, Ingo Molnar <mingo@elte.hu>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cancel_delayed_work: use del_timer() instead of del_timer_sync()
Date: Thu, 26 Apr 2007 19:29:53 +0400	[thread overview]
Message-ID: <20070426152953.GA1824@tv-sign.ru> (raw)
In-Reply-To: <20070426142921.GE3145@ff.dom.local>

On 04/26, Jarek Poplawski wrote:
>
> On Wed, Apr 25, 2007 at 04:52:14PM +0400, Oleg Nesterov wrote:
> > 
> > >                                                  It seems this
> > > change cannot do any harm, but anyway it could change a few
> > > things, e.g. with current version of cancel_rearming_delayed_work
> > > some flush_workqueue could be done needlessly, before the work
> > > is queued from timer.
> > 
> > I don't think so... Could you clarify?
> 
> With a code like:
> 
> if (!cancel_delayed_work(dwork))
> 	flush_workqueue(wq);
> 	
> if cancel_ returns 0, and there is _queue_work in progress,
> flush_ will be done once, after this work is queued.
> 
> After the patch, and the same situation flush_ also runs
> one time, but maybe without the work in a queue.

First, this is very unlikely event, and the behaviour is correct,
do you agree?

Even in this case, it is very unlikely that flush_cpu_workqueue()
will take cwq->lock before extremely short delayed_work_timer_fn.

Even if it does, work->func() likely will be completed when the
caller of flush_workqueue() will be woken by run_workquue() and
gets CPU.

Please also look at http://marc.info/?t=117699337200022&r=1

> > >                       It's not a big deal here, but if anybody
> > > did something like this without loop - it could matter.
> > > 
> > > So, probably a lot of current code should be checked, before
> > > applying and I doubt the gain is worth of this. Maybe, for
> > > safety, make this with new name as an alternative and
> > > deprecate the current version?
> > 
> > This change should not make any visible difference for the callers,
> > otherwise it is buggy.
> 
> IMHO, there is the same visible difference,
> as between del_timer and del_timer_sync.

Jarek, please, could you be more explicite ? del_timer() and
del_timer_sync() are different in many ways. What exactly will
impact the user of cancel_delaye_work ?

Oleg.


  reply	other threads:[~2007-04-26 16:24 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-04-24 21:50 Oleg Nesterov
2007-04-25 10:04 ` David Howells
2007-04-25 13:02 ` Jarek Poplawski
2007-04-25 12:52   ` Oleg Nesterov
2007-04-26 14:29     ` Jarek Poplawski
2007-04-26 15:29       ` Oleg Nesterov [this message]
2007-04-27  6:15         ` Jarek Poplawski
2007-04-27  7:23           ` Oleg Nesterov

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=20070426152953.GA1824@tv-sign.ru \
    --to=oleg@tv-sign.ru \
    --cc=akpm@linux-foundation.org \
    --cc=davem@davemloft.net \
    --cc=dhowells@redhat.com \
    --cc=jarkao2@o2.pl \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@elte.hu \
    --subject='Re: [PATCH] cancel_delayed_work: use del_timer() instead of del_timer_sync()' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).