Re: [PATCH] mm: Check for SIGKILL inside dup_mmap() loop.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> On Thu 29-03-18 14:30:03, Andrew Morton wrote:
> [...]
> > Dumb question: if a thread has been oom-killed and then tries to
> > allocate memory, should the page allocator just fail the allocation
> > attempt?  I suppose there are all sorts of reasons why not :(
> 
> We give those tasks access to memory reserves to move on (see
> oom_reserves_allowed) and fail allocation if reserves do not help
> 
> 	if (tsk_is_oom_victim(current) &&
> 	    (alloc_flags == ALLOC_OOM ||
> 	     (gfp_mask & __GFP_NOMEMALLOC)))
> 		goto nopage;
> So we...
> 
> > In which case, yes, setting a new
> > PF_MEMALLOC_MAY_FAIL_IF_I_WAS_OOMKILLED around such code might be a
> > tidy enough solution.  It would be a bit sad to add another test in the
> > hot path (should_fail_alloc_page()?), but geeze we do a lot of junk
> > already.
> 
> ... do not need this.

Excuse me? But that check is after

	/* Reclaim has failed us, start killing things */
	page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress);
	if (page)
		goto got_pg;

which means that tsk_is_oom_victim(current) && alloc_flags == ALLOC_OOM threads
can still trigger the OOM killer as soon as the OOM reaper sets MMF_OOM_SKIP.