linux-kernel - Re: [PATCH v2] cgroup: disable irqs while holding css_set

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Message-ID: <cf514889-8a4d-1ef4-cf4a-fd1a9b9bcb1d@redhat.com>
Date:	Thu, 16 Jun 2016 21:12:32 -0300
From:	Daniel Bristot de Oliveira <daolivei@...hat.com>
To:	Tejun Heo <tj@...nel.org>,
	Daniel Bristot de Oliveira <daolivei@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	"Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Juri Lelli <juri.lelli@....com>, cgroups@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2] cgroup: disable irqs while holding css_set_lock

On 06/16/2016 07:14 PM, Tejun Heo wrote:
> Except that the patch seems to use irqsave/restore instead of plain
> irq ones in places.  Care to update those?

Hi Tejun,

The use of the irq spin_(un)lock_irq() assumes that the code is always
called with IRQs enabled. But that is not always true in this case, as
we call cgroup_free() in the hard IRQ context, and unconditionally
enable IRQ in this context is a problem. So we need to use irqsave/restore.

Discussing with rostedt, we figured that this needs to be IRQ safe
(using irqsave/restore) in the PREEMPT RT too, so I need to code a v3 of
this patch using raw_spin_*() functions to avoid this problem in the -rt
kernel as well.

Do you see any problems on this?

Thanks! -- Daniel