On 08/02/2012 10:16 AM, Michal Hocko wrote:
Hi Andrew, the following patch fixes yet-another race in the hugetlb pte sharing code reported by Larry. It is based on top of the current -mm tree but it cleanly applies to linus tree as well. It should go to stable as well. The bug is there for ages but this fix is possible only since 3.0 because i_mmap_lock used to be a spinlock until 3d48ae45 which turned it into mutex and so we can call pmd_alloc.
This patch addresses the issue by moving pmd_alloc into huge_pmd_share which guarantees that the shared pud is populated in the same critical section as pmd. This also means that huge_pte_offset test in huge_pmd_share is serialized correctly now which in turn means that the success of the sharing will be higher as the racing tasks see the pud and pmd populated together. Race identified and changelog written mostly by Mel Gorman Reported-and-tested-by: Larry Woodman <lwoodman@xxxxxxxxxx> Reviewed-by: Mel Gorman <mgorman@xxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>