From: john stultz <johnstul@us.ibm.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH -rt] Fix TASKLET_STATE_SCHED WARN_ON()
Date: Fri, 15 Jun 2007 14:51:11 -0700 [thread overview]
Message-ID: <1181944271.5998.15.camel@localhost.localdomain> (raw)
In-Reply-To: <20070615155231.GA345@tv-sign.ru>
On Fri, 2007-06-15 at 19:52 +0400, Oleg Nesterov wrote:
> john stultz wrote:
> >
> > The following additional patch should correct this issue. Although since
> > we weren't actually hitting it, the issue is a bit theoretical, so I've
> > not been able to prove it really fixes anything.
>
> Could you please look at the message below? I sent it privately near a month
> ago, but I think these problems are not fixed yet.
Hmm. Maybe you sent it to others on the cc list, as I can't find it in
my box. But apologies anyway.
> ---------------------------------------------------------------------------
>
> > +__tasklet_action(struct softirq_action *a, struct tasklet_struct *list)
> > +{
> > + int loops = 1000000;
> >
> > while (list) {
> > struct tasklet_struct *t = list;
> >
> > list = list->next;
> > + /*
> > + * Should always succeed - after a tasklist got on the
> > + * list (after getting the SCHED bit set from 0 to 1),
> > + * nothing but the tasklet softirq it got queued to can
> > + * lock it:
> > + */
> > + if (!tasklet_trylock(t)) {
> > + WARN_ON(1);
> > + continue;
> > + }
> > +
> > + t->next = NULL;
> > +
> > + /*
> > + * If we cannot handle the tasklet because it's disabled,
> > + * mark it as pending. tasklet_enable() will later
> > + * re-schedule the tasklet.
> > + */
> > + if (unlikely(atomic_read(&t->count))) {
> > +out_disabled:
> > + /* implicit unlock: */
> > + wmb();
> > + t->state = TASKLET_STATEF_PENDING;
>
> What if tasklet_enable() happens just before this line ?
>
> After the next schedule_tasklet() we have all bits set: SCHED, RUN, PENDING.
> The next invocation of __tasklet_action() clears SCHED, but tasklet_tryunlock()
> below can never succeed because of PENDING.
Yep. I've only been focusing on races in schedule/action, as I've been
hunting issues w/ rcu. But I'll agree that the other state changes look
problematic. I know Paul McKenney was looking at some of the other state
changes and was seeing some potential problems as well.
thanks
-john
next prev parent reply other threads:[~2007-06-15 21:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-15 15:52 [PATCH -rt] Fix TASKLET_STATE_SCHED WARN_ON() Oleg Nesterov
2007-06-15 21:51 ` john stultz [this message]
2007-06-15 23:59 ` Oleg Nesterov
-- strict thread matches above, loose matches on Subject: below --
2007-06-06 2:17 john stultz
2007-06-06 9:45 ` Ingo Molnar
2007-06-06 17:39 ` john stultz
2007-06-06 10:31 ` Jesper Juhl
2007-06-14 21:20 ` john stultz
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=1181944271.5998.15.camel@localhost.localdomain \
--to=johnstul@us.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=oleg@tv-sign.ru \
--cc=paulmck@linux.vnet.ibm.com \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/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 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).