Messages in this thread | | | From | "Zi Yan" <> | Subject | Re: [PATCH] mm, numa: Fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot_numa | Date | Mon, 10 Apr 2017 12:49:40 -0500 |
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On 10 Apr 2017, at 12:20, Mel Gorman wrote:
> On Mon, Apr 10, 2017 at 11:45:08AM -0500, Zi Yan wrote: >>> While this could be fixed with heavy locking, it's only necessary to >>> make a copy of the PMD on the stack during change_pmd_range and avoid >>> races. A new helper is created for this as the check if quite subtle and the >>> existing similar helpful is not suitable. This passed 154 hours of testing >>> (usually triggers between 20 minutes and 24 hours) without detecting bad >>> PMDs or corruption. A basic test of an autonuma-intensive workload showed >>> no significant change in behaviour. >>> >>> Signed-off-by: Mel Gorman <mgorman@techsingularity.net> >>> Cc: stable@vger.kernel.org >> >> Does this patch fix the same problem fixed by Kirill's patch here? >> https://lkml.org/lkml/2017/3/2/347 >> > > I don't think so. The race I'm concerned with is due to locks not being > held and is in a different path.
I do not agree. Kirill's patch is fixing the same race problem but in zap_pmd_range().
The original autoNUMA code first clears PMD then sets it to protnone entry. pmd_trans_huge() does not return TRUE because it saw cleared PMD, but pmd_none_or_clear_bad() later saw the protnone entry and reported it as bad. Is this the problem you are trying solve?
Kirill's patch will pmdp_invalidate() the PMD entry, which keeps _PAGE_PSE bit, so pmd_trans_huge() will return TRUE. In this case, it also fixes your race problem in change_pmd_range().
Let me know if I miss anything.
Thanks.
-- Best Regards Yan Zi [unhandled content-type:application/pgp-signature] | |