linux-kernel - Re: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to async page fault

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAFTL4hy1PB3u+i3xEXvz0Zt4kNQx9ioAHaM2BPMfXiNm7Koxmg@mail.gmail.com>
Date:	Tue, 27 Nov 2012 23:53:07 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Li Zhong <zhong@...ux.vnet.ibm.com>,
	linux-next list <linux-next@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com,
	sasha.levin@...cle.com, avi@...hat.com
Subject: Re: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to
 async page fault

2012/11/27 Gleb Natapov <gleb@...hat.com>:
> What is the semantics of enter_idle()/exit_idle(), what are they used for?

It's used by drivers/idle/i7300_idle.c for some tracking. I don't know much
the details.

enter_idle() is called right before the CPU is set to lower power mode: hlt()

exit_idle() is called anytime we exit this low power mode: irq,
polling on need_resched(), etc...

> Not present fault happening in idle task does not mean we exit idle
> task. If this happens exception handler will execute sti; hlt waiting
> for missing page to be ready. Any interrupt happening during this hlt
> will do exit_idle() by itself.

Well, the code executed by this fault should be considered as an exit
from idle mode. Now it's a small piece of code and we hlt() quickly so
I guess getting of idle_exit() there wouldn't hurt much.

It's buggy for now anyway due to that race where we may not have an
opportunity to call back idle_enter() if the fault happens between the
idle_enter() in the idle loop and the hlt() in the idle loop.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/