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

Colin Cross ccross at android.com
Sun Nov 21 15:02:28 PST 2010

On Sat, Nov 20, 2010 at 6:00 PM, Colin Cross <ccross at android.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 at android.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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