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

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Message-ID: <20160617053625.GL31708@htj.duckdns.org>
Date:	Fri, 17 Jun 2016 01:36:25 -0400
From:	Tejun Heo <tj@...nel.org>
To:	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

Hello,

On Thu, Jun 16, 2016 at 09:12:32PM -0300, Daniel Bristot de Oliveira wrote:
> 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?

Use of raw_spin is fine but I don't see how, say, rebind_subsystems()
or cgroup_setup_root() can ever be called with irq disabled given that
they assume sleepable context.  Please use _irq and _irqsave
appropriately depending on the circumstances.

Thanks.

-- 
tejun