[PATCH] android,lowmemorykiller: Don't abuse TIF_MEMDIE.

[Greg KH]

On Mon, Mar 21, 2016 at 08:00:49PM +0900, Tetsuo Handa wrote:
> Greg Kroah-Hartman wrote:
> > On Tue, Mar 08, 2016 at 03:18:59PM +0100, Michal Hocko wrote:
> > > On Tue 08-03-16 20:01:32, Tetsuo Handa wrote:
> > > > Currently, lowmemorykiller (LMK) is using TIF_MEMDIE for two purposes.
> > > > One is to remember processes killed by LMK, and the other is to
> > > > accelerate termination of processes killed by LMK.
> > > > 
> > > > But since LMK is invoked as a memory shrinker function, there still
> > > > should be some memory available. It is very likely that memory
> > > > allocations by processes killed by LMK will succeed without using
> > > > ALLOC_NO_WATERMARKS via TIF_MEMDIE. Even if their allocations cannot
> > > > escape from memory allocation loop unless they use ALLOC_NO_WATERMARKS,
> > > > lowmem_deathpending_timeout can guarantee forward progress by choosing
> > > > next victim process.
> > > > 
> > > > On the other hand, mark_oom_victim() assumes that it must be called with
> > > > oom_lock held and it must not be called after oom_killer_disable() was
> > > > called. But LMK is calling it without holding oom_lock and checking
> > > > oom_killer_disabled. It is possible that LMK calls mark_oom_victim()
> > > > due to allocation requests by kernel threads after current thread
> > > > returned from oom_killer_disabled(). This will break synchronization
> > > > for PM/suspend.
> > > > 
> > > > This patch introduces per a task_struct flag for remembering processes
> > > > killed by LMK, and replaces TIF_MEMDIE with that flag. By applying this
> > > > patch, assumption by mark_oom_victim() becomes true.
> > > 
> > > Thanks for looking into this. A separate flag sounds like a better way
> > > to go (assuming that the flags are not scarce which doesn't seem to be
> > > the case here).
> > >  
> > > The LMK cannot kill the frozen tasks now but this shouldn't be a big deal
> > > because this is not strictly necessary for the system to move on. We are
> > > not OOM.
> > > 
> > > > Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> > > > Cc: Michal Hocko <mhocko at suse.cz>
> > > > Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> > > > Cc: Arve Hjonnevag <arve at android.com>
> > > > Cc: Riley Andrews <riandrews at android.com>
> > > 
> > > Acked-by: Michal Hocko <mhocko at suse.com>
> > 
> > So, any objection for me taking this through the staging tree?
> > 
> Seems no objection. Please take this through the staging tree.

Ok, will do so after 4.6-rc1 is out.