Re: [PATCH 1/6] proc, oom: drop bogus task_lock and mm check

From: Vladimir Davydov
Date: Mon May 30 2016 - 10:22:08 EST

On Mon, May 30, 2016 at 03:05:51PM +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> both oom_adj_write and oom_score_adj_write are using task_lock,
> check for task->mm and fail if it is NULL. This is not needed because
> the oom_score_adj is per signal struct so we do not need mm at all.
> The code has been introduced by 3d5992d2ac7d ("oom: add per-mm oom
> disable count") but we do not do per-mm oom disable since c9f01245b6a7
> ("oom: remove oom_disable_count").
> The task->mm check is even not correct because the current thread might
> have exited but the thread group might be still alive - e.g. thread
> group leader would lead that echo $VAL > /proc/pid/oom_score_adj would
> always fail with EINVAL while /proc/pid/task/$other_tid/oom_score_adj
> would succeed. This is unexpected at best.
> Remove the lock along with the check to fix the unexpected behavior
> and also because there is not real need for the lock in the first place.
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Reviewed-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>