linux-kernel - Re: [PATCH 2/5] mm: compaction: reset cached scanner pfn's before reading them

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: <52949F1C.2060607@redhat.com>
Date:	Tue, 26 Nov 2013 08:16:12 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Vlastimil Babka <vbabka@...e.cz>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 2/5] mm: compaction: reset cached scanner pfn's before
 reading them

On 11/25/2013 09:26 AM, Vlastimil Babka wrote:
> Compaction caches pfn's for its migrate and free scanners to avoid scanning
> the whole zone each time. In compact_zone(), the cached values are read to
> set up initial values for the scanners. There are several situations when
> these cached pfn's are reset to the first and last pfn of the zone,
> respectively. One of these situations is when a compaction has been deferred
> for a zone and is now being restarted during a direct compaction, which is also
> done in compact_zone().
> 
> However, compact_zone() currently reads the cached pfn's *before* resetting
> them. This means the reset doesn't affect the compaction that performs it, and
> with good chance also subsequent compactions, as update_pageblock_skip() is
> likely to be called and update the cached pfn's to those being processed.
> Another chance for a successful reset is when a direct compaction detects that
> migration and free scanners meet (which has its own problems addressed by
> another patch) and sets update_pageblock_skip flag which kswapd uses to do the
> reset because it goes to sleep.
> 
> This is clearly a bug that results in non-deterministic behavior, so this patch
> moves the cached pfn reset to be performed *before* the values are read.
> 
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rik van Riel <riel@...hat.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Rik van Riel <riel@...hat.com>

-- 
All rights reversed
--
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/