linux-kernel - Re: [PATCH 2/6] mm: add get_pageblock_migratetype_nolock() for cases where locking is undesirable

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: <20140305003709.GB2340@lge.com>
Date:	Wed, 5 Mar 2014 09:37:10 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 2/6] mm: add get_pageblock_migratetype_nolock() for cases
 where locking is undesirable

On Fri, Feb 28, 2014 at 03:15:00PM +0100, Vlastimil Babka wrote:
> In order to prevent race with set_pageblock_migratetype, most of calls to
> get_pageblock_migratetype have been moved under zone->lock. For the remaining
> call sites, the extra locking is undesirable, notably in free_hot_cold_page().
> 
> This patch introduces a _nolock version to be used on these call sites, where
> a wrong value does not affect correctness. The function makes sure that the
> value does not exceed valid migratetype numbers. Such too-high values are
> assumed to be a result of race and caller-supplied fallback value is returned
> instead.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  include/linux/mmzone.h | 24 ++++++++++++++++++++++++
>  mm/compaction.c        | 14 +++++++++++---
>  mm/memory-failure.c    |  3 ++-
>  mm/page_alloc.c        | 22 +++++++++++++++++-----
>  mm/vmstat.c            |  2 +-
>  5 files changed, 55 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index fac5509..7c3f678 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -75,6 +75,30 @@ enum {
>  
>  extern int page_group_by_mobility_disabled;
>  
> +/*
> + * When called without zone->lock held, a race with set_pageblock_migratetype
> + * may result in bogus values. Use this variant only when this does not affect
> + * correctness, and taking zone->lock would be costly. Values >= MIGRATE_TYPES
> + * are considered to be a result of this race and the value of race_fallback
> + * argument is returned instead.
> + */
> +static inline int get_pageblock_migratetype_nolock(struct page *page,
> +	int race_fallback)
> +{
> +	int ret = get_pageblock_flags_group(page, PB_migrate, PB_migrate_end);
> +
> +	if (unlikely(ret >= MIGRATE_TYPES))
> +		ret = race_fallback;
> +
> +	return ret;
> +}

How about below forms?

get_pageblock_migratetype_locked(struct page *page)
get_pageblock_migratetype(struct page *page, int race_fallback)

get_pageblock_migratetype() and _nolock looks error-prone because developer
who try to use get_pageblock_migratetype() may not know that it needs lock.

Thanks.
--
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/