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SubjectRe: [PATCH 3/5] oom: introduce find_lock_task_mm() to fix !mm false positives
On Mon, 31 May 2010, KOSAKI Motohiro wrote:

> From: Oleg Nesterov <oleg@redhat.com>
> Subject: [PATCH 3/5] oom: introduce find_lock_task_mm() to fix !mm false positives
>
> Almost all ->mm == NUL checks in oom_kill.c are wrong.
>
> The current code assumes that the task without ->mm has already
> released its memory and ignores the process. However this is not
> necessarily true when this process is multithreaded, other live
> sub-threads can use this ->mm.
>
> - Remove the "if (!p->mm)" check in select_bad_process(), it is
> just wrong.
>
> - Add the new helper, find_lock_task_mm(), which finds the live
> thread which uses the memory and takes task_lock() to pin ->mm
>
> - change oom_badness() to use this helper instead of just checking
> ->mm != NULL.
>
> - As David pointed out, select_bad_process() must never choose the
> task without ->mm, but no matter what badness() returns the
> task can be chosen if nothing else has been found yet.
>
> Note! This patch is not enough, we need more changes.
>
> - badness() was fixed, but oom_kill_task() still ignores
> the task without ->mm
>
> This will be addressed later.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Cc: David Rientjes <rientjes@google.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [rebase
> latest -mm and remove some obsoleted description]

This is already pushed as part of my oom killer rewrite in patch 15/18
"oom: introduce find_lock_task_mm to fix !mm false positives".


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