linux-kernel - Re: [PATCH] mm, oom: Give __GFP_NOFAIL allocations access to memory reserves

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20151124195710.GA12923@cmpxchg.org>
Date:	Tue, 24 Nov 2015 14:57:10 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, oom: Give __GFP_NOFAIL allocations access to memory
 reserves

On Tue, Nov 24, 2015 at 06:02:39PM +0100, Michal Hocko wrote:
> On Tue 24-11-15 11:26:04, Johannes Weiner wrote:
> > On Tue, Nov 24, 2015 at 10:47:09AM +0100, Michal Hocko wrote:
> > > Besides that there is no other reliable warning that we are getting
> > > _really_ short on memory unlike when the allocation failure is
> > > allowed. OOM killer report might be missing because there was no actual
> > > killing happening.
> > 
> > This is why I would like to see that warning generalized, and not just
> > for __GFP_NOFAIL. We have allocations other than explicit __GFP_NOFAIL
> > that will loop forever in the allocator,
> 
> Yes but does it make sense to warn for all of them? Wouldn't it be
> sufficient to warn about those which cannot allocate anything even
> though they are doing ALLOC_NO_WATERMARKS?

Why is it important whether they can do ALLOC_NO_WATERMARKS or not?

I'm worried about all those that can loop forever with locks held.

> > and when this deadlocks the
> > machine all we see is other tasks hanging, but not the culprit. If we
> > were to get a backtrace of some task in the allocator that is known to
> > hold locks, suddenly all the other hung tasks will make sense, and it
> > will clearly distinguish such an allocator deadlock from other issues.
> 
> Tetsuo was suggesting a more sophisticated infrastructure for tracking
> allocations [1] which take too long without making progress. I haven't
> seen his patch because I was too busy with other stuff but maybe this is
> what you would like to see?

That seems a bit excessive. I was thinking something more like this:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 05ef7fb..fbfc581 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3004,6 +3004,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	enum migrate_mode migration_mode = MIGRATE_ASYNC;
 	bool deferred_compaction = false;
 	int contended_compaction = COMPACT_CONTENDED_NONE;
+	unsigned int nr_tries = 0;
 
 	/*
 	 * In the slowpath, we sanity check order to avoid ever trying to
@@ -3033,6 +3034,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 		goto nopage;
 
 retry:
+	if (++nr_retries % 100 == 0)
+		warn_alloc_failed(gfp_mask, order, "Potential GFP deadlock\n");
+
 	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
 		wake_all_kswapds(order, ac);
 
> Anyway I would like to make some progress on this patch. Do you think
> that it would be acceptable in the current form without the warning or
> you preffer a different way?

Oh, I have nothing against your patch, please go ahead with it. I just
wondered out loud when you proposed a warning about deadlocking NOFAIL
allocations but limited it to explicit __GFP_NOFAIL allocations, when
those obviously aren't the only ones that can deadlock in that way.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/