linux-kernel - Re: [PATCH v2] mm/cma: fix alloc_contig

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Date:   Wed, 29 Nov 2017 14:38:17 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Nazarewicz <mina86@...a86.com>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] mm/cma: fix alloc_contig_range ret code/potential leak

On Wed, Nov 22, 2017 at 10:52:14AM -0800, Mike Kravetz wrote:
> If the call __alloc_contig_migrate_range() in alloc_contig_range
> returns -EBUSY, processing continues so that test_pages_isolated()
> is called where there is a tracepoint to identify the busy pages.
> However, it is possible for busy pages to become available between
> the calls to these two routines.  In this case, the range of pages
> may be allocated.   Unfortunately, the original return code (ret
> == -EBUSY) is still set and returned to the caller.  Therefore,
> the caller believes the pages were not allocated and they are leaked.
> 
> Update comment to indicate that allocation is still possible even if
> __alloc_contig_migrate_range returns -EBUSY.  Also, clear return code
> in this case so that it is not accidentally used or returned to caller.
> 
> Fixes: 8ef5849fa8a2 ("mm/cma: always check which page caused allocation failure")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Good catch!!

Acked-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Thanks.