Re: [PATCH 08/63] mm: Close races between THP migration and PMD numaclearing

[Rik van Riel]

On 10/07/2013 06:28 AM, Mel Gorman wrote:
> THP migration uses the page lock to guard against parallel allocations
> but there are cases like this still open
> 
> Task A						Task B
> do_huge_pmd_numa_page				do_huge_pmd_numa_page
> lock_page
> mpol_misplaced == -1
> unlock_page
> goto clear_pmdnuma
> 						lock_page
> 						mpol_misplaced == 2
> 						migrate_misplaced_transhuge
> pmd = pmd_mknonnuma
> set_pmd_at
> 
> During hours of testing, one crashed with weird errors and while I have
> no direct evidence, I suspect something like the race above happened.
> This patch extends the page lock to being held until the pmd_numa is
> cleared to prevent migration starting in parallel while the pmd_numa is
> being cleared. It also flushes the old pmd entry and orders pagetable
> insertion before rmap insertion.
> 
> Cc: stable <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

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