Re: [patch v2 2/2] oom: kill all threads sharing oom killed task's mm

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 16 Aug 2010 18:16:08 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> It's necessary to kill all threads that share an oom killed task's mm if
> the goal is to lead to future memory freeing.
> 
> This patch reintroduces the code removed in 8c5cd6f3 (oom: oom_kill
> doesn't kill vfork parent (or child)) since it is obsoleted.
> 
> It's now guaranteed that any task passed to oom_kill_task() does not
> share an mm with any thread that is unkillable.  Thus, we're safe to
> issue a SIGKILL to any thread sharing the same mm.
> 
> This is especially necessary to solve an mm->mmap_sem livelock issue
> whereas an oom killed thread must acquire the lock in the exit path while
> another thread is holding it in the page allocator while trying to
> allocate memory itself (and will preempt the oom killer since a task was
> already killed).  Since tasks with pending fatal signals are now granted
> access to memory reserves, the thread holding the lock may quickly
> allocate and release the lock so that the oom killed task may exit.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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