From: Peter Zijlstra <peterz@infradead.org>
To: Kirill Tkhai <tkhai@yandex.ru>
Cc: linux-kernel@vger.kernel.org, Kirill Tkhai <ktkhai@parallels.com>,
Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@gmail.com>
Subject: Re: [PATCH v2 1/3] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl()
Date: Thu, 2 Oct 2014 11:34:08 +0200 [thread overview]
Message-ID: <20141002093408.GB2849@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20140930210412.5258.35299.stgit@localhost>
On Wed, Oct 01, 2014 at 01:04:22AM +0400, Kirill Tkhai wrote:
> From: Kirill Tkhai <ktkhai@parallels.com>
>
> hrtimer_try_to_cancel() may bring a suprise, its call may fail.
Well, not really a surprise that, its a _try_ operation after all.
> raw_spin_lock(&rq->lock)
> ... dl_task_timer raw_spin_lock(&rq->lock)
> ... raw_spin_lock(&rq->lock) ...
> switched_from_dl() ... ...
> hrtimer_try_to_cancel() ... ...
> switched_to_fair() ... ...
> ... ... ...
> ... ... ...
> raw_spin_unlock(&rq->lock) ... (asquired)
> ... ... ...
> ... ... ...
> do_exit() ... ...
> schedule() ... ...
> raw_spin_lock(&rq->lock) ... raw_spin_unlock(&rq->lock)
> ... ... ...
> raw_spin_unlock(&rq->lock) ... raw_spin_lock(&rq->lock)
> ... ... (asquired)
> put_task_struct() ... ...
> free_task_struct() ... ...
> ... ... raw_spin_unlock(&rq->lock)
> ... (asquired) ...
> ... ... ...
> ... Surprise!!! ...
>
> So, let's implement 100% guaranteed way to cancel the timer and let's
> be sure we are safe even in very unlikely situations.
>
> We do not create any problem with rq unlocking, because it already
> may happed below in pull_dl_task(). No problem with deadline tasks
> balancing too.
That doesn't sound right. pull_dl_task() is an entirely different
callchain than switched_from(). Now it might still be fine, but you
cannot compare it with pull_dl_task.
next prev parent reply other threads:[~2014-10-02 9:34 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-30 21:04 [PATCH v2 1/3] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl() Kirill Tkhai
2014-09-30 21:04 ` [PATCH v2 2/3] sched/dl: Cleanup prio_changed_dl() Kirill Tkhai
2014-10-02 9:36 ` Peter Zijlstra
2014-10-02 9:52 ` Kirill Tkhai
2014-10-21 16:24 ` Juri Lelli
2014-10-21 16:33 ` Kirill Tkhai
2014-10-22 9:33 ` Juri Lelli
2014-10-23 23:04 ` Wanpeng Li
2014-10-24 9:26 ` Juri Lelli
2014-09-30 21:04 ` [PATCH v2 3/3] sched/fair: Delete resched_cpu() from idle_balance() Kirill Tkhai
2014-10-03 5:28 ` [tip:sched/core] " tip-bot for Kirill Tkhai
2014-10-02 9:34 ` Peter Zijlstra [this message]
2014-10-02 10:05 ` [PATCH v2 1/3] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl() Kirill Tkhai
2014-10-21 10:30 ` Juri Lelli
2014-10-21 10:48 ` Kirill Tkhai
2014-10-21 11:41 ` Juri Lelli
2014-10-21 14:21 ` Kirill Tkhai
2014-10-22 10:00 ` Juri Lelli
2014-10-23 8:39 ` Kirill Tkhai
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=20141002093408.GB2849@worktop.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=juri.lelli@gmail.com \
--cc=ktkhai@parallels.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=tkhai@yandex.ru \
/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.