From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: [PATCH] cgroup: make cgrp->event_list_lock irqsafe Date: Wed, 6 Mar 2013 15:15:59 +0800 Message-ID: <5136ED2F.8080400@huawei.com> References: <5136B7C1.6030403@huawei.com> <20130306062224.GJ1227@htj.dyndns.org> <5136E9A4.7000201@huawei.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Tejun Heo Cc: "Kirill A. Shutemov" , LKML , Cgroups On 2013/3/6 15:02, Tejun Heo wrote: > On Tue, Mar 5, 2013 at 11:00 PM, Li Zefan wrote: >>> Why should wqh->lock be hard-irq-safe? Is it actually grabbed from >>> irq context? >> >> becase cgroup_event_wake() is a callback to a wait queue, and it's wake_up() >> that acquires wqh->lock with irq disabled. > > So, acquiring a lock with irq disabled doesn't make it a irq lock. > Being grabbed *from* irq handler makes it a irq lock. Would the > wake_up() happen from irq handler? > wqh->lock is used through out fs/eventfd.c. I don't know if currently there's any kernel user using eventfd APIs in an irq handler, but at least that should be allowed. wake_up() is also allowed to be called from irq handler? "allowed" should be enough reason we forbid: spin_lock_irqsave(...) spin_lock(...)