linux-kernel - [PATCH] hugetlb: clarify hugetlb_instantiation

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Message-ID: <20111121144608.GC16957@tiehlicka.suse.cz>
Date:	Mon, 21 Nov 2011 15:46:08 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] hugetlb: clarify hugetlb_instantiation_mutex usage

And the follow up documentation patch:
---
>From 51bef05e4cbf97a749e6c0245114eceb21d05d61 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.cz>
Date: Mon, 21 Nov 2011 15:39:45 +0100
Subject: [PATCH] hugetlb: clarify hugetlb_instantiation_mutex usage

Let's make it clear that we cannot race with other fault handlers due to
hugetlb (global) mutex.
Also make it clear that we want to keep pte_same checks anayway to have a
transition from the global mutex easier.

Signed-off-by: Michal Hocko <mhocko@...e.cz>
---
 mm/hugetlb.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f76c7ea..611cdc8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2348,6 +2348,9 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 
 /*
  * Hugetlb_cow() should be called with page lock of the original hugepage held.
+ * Called with hugetlb_instantiation_mutex held and pte_page locked so we
+ * cannot race with other handlers or page migration.
+ * Keep the pte_same checks anyway to make transition from the mutex easier.
  */
 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
 			unsigned long address, pte_t *ptep, pte_t pte,
-- 
1.7.7.1


-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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