From: Xunlei Pang <xpang@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>,
xlpang@redhat.com,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
stable@vger.kernel.org
Subject: Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair
Date: Mon, 11 Jul 2016 20:12:24 +0800 [thread overview]
Message-ID: <57838D28.4090003@redhat.com> (raw)
In-Reply-To: <CANRm+CxTudRZWv9oU3XU+8=f+FrVRUcT-EeDVems90F9+NdEyg@mail.gmail.com>
On 2016/07/11 at 17:54, Wanpeng Li wrote:
> Hi Konstantin, Xunlei,
> 2016-07-11 16:42 GMT+08:00 Xunlei Pang <xpang@redhat.com>:
>> On 2016/07/11 at 16:22, Xunlei Pang wrote:
>>> On 2016/07/11 at 15:25, Wanpeng Li wrote:
>>>> 2016-06-16 20:57 GMT+08:00 Konstantin Khlebnikov <khlebnikov@yandex-team.ru>:
>>>>> Hierarchy could be already throttled at this point. Throttled next
>>>>> buddy could trigger null pointer dereference in pick_next_task_fair().
>>>> There is cfs_rq->next check in pick_next_entity(), so how can null
>>>> pointer dereference happen?
>>> I guess it's the following code leading to a NULL se returned:
>> s/NULL/empty-entity cfs_rq se/
>>
>>> pick_next_entity():
>>> if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
> ^^^^^^^^^^^^^
> I think this will return false.
With the wrong throttled_hierarchy(), I think this can happen. But after we have the
corrected throttled_hierarchy() patch, I can't see how it is possible.
dequeue_task_fair():
if (task_sleep && parent_entity(se))
set_next_buddy(parent_entity(se));
How does dequeue_task_fair() with DEQUEUE_SLEEP set(true task_sleep) happen to a throttled hierarchy?
IOW, a task belongs to a throttled hierarchy is running?
Maybe Konstantin knows the reason.
Regards,
Xunlei
next prev parent reply other threads:[~2016-07-11 12:12 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-16 12:57 [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair Konstantin Khlebnikov
2016-06-16 17:06 ` bsegall
2016-06-21 13:44 ` Konstantin Khlebnikov
2016-06-24 9:00 ` [tip:sched/urgent] sched/fair: Do not announce throttled next buddy in dequeue_task_fair() tip-bot for Konstantin Khlebnikov
2016-07-11 7:25 ` [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair Wanpeng Li
2016-07-11 8:15 ` Konstantin Khlebnikov
2016-07-11 8:22 ` Xunlei Pang
2016-07-11 8:42 ` Xunlei Pang
2016-07-11 9:54 ` Wanpeng Li
2016-07-11 12:12 ` Xunlei Pang [this message]
2016-07-11 12:26 ` Konstantin Khlebnikov
2016-07-12 17:25 ` bsegall
2016-07-13 1:50 ` Wanpeng Li
2016-07-13 1:58 ` Xunlei Pang
2016-07-13 2:14 ` Wanpeng Li
2016-07-13 17:06 ` bsegall
2016-07-14 12:11 ` Wanpeng Li
2016-07-14 17:54 ` bsegall
2016-07-14 22:30 ` Wanpeng Li
2016-07-14 22:49 ` bsegall
2016-07-14 23:03 ` Wanpeng Li
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=57838D28.4090003@redhat.com \
--to=xpang@redhat.com \
--cc=kernellwp@gmail.com \
--cc=khlebnikov@yandex-team.ru \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=stable@vger.kernel.org \
--cc=xlpang@redhat.com \
/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).