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From: Daniel Bristot de Oliveira <daolivei@redhat.com>
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Subject: Re: [PATCH v2] cgroup: disable irqs while holding css_set_lock
To: Tejun Heo <tj@kernel.org>,
        Daniel Bristot de Oliveira <daolivei@redhat.com>
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Cc: linux-kernel@vger.kernel.org, Rik van Riel <riel@redhat.com>,
        "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>,
        Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>,
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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