linux-kernel - Re: [PATCH] cgroup: Remove RCU from task->cgroups

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Message-ID: <AANLkTikx6d0_VFtZ4zWQucRCf=vFt7N2M6=0jpnKasEE@mail.gmail.com>
Date:	Sun, 21 Nov 2010 15:02:28 -0800
From:	Colin Cross <ccross@...roid.com>
To:	linux-kernel@...r.kernel.org
Cc:	Colin Cross <ccross@...roid.com>, Paul Menage <menage@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH] cgroup: Remove RCU from task->cgroups

On Sat, Nov 20, 2010 at 6:00 PM, Colin Cross <ccross@...roid.com> wrote:
> The synchronize_rcu call in cgroup_attach_task can be very
> expensive.  All fastpath accesses to task->cgroups already
> use task_lock() or cgroup_lock() to protect against updates,
> and only the CGROUP_DEBUG files have RCU read-side critical
> sections.
>
> This patch replaces rcu_read_lock() with task_lock(current)
> around the debug file acceses to current->cgroups and removes
> the synchronize_rcu call in cgroup_attach_task.
>
> Signed-off-by: Colin Cross <ccross@...roid.com>
> ---
>  kernel/cgroup.c |   22 ++++++++--------------
>  1 files changed, 8 insertions(+), 14 deletions(-)
>

This patch isn't correct, there's an rcu_dereference I missed inside
task_group(), and that's the important one.
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