linux-kernel - [PATCH] [6/31] HWPOISON: avoid grabbing the page count multiple times during madvise injection

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Message-Id: <20091208211622.54209B151F@basil.firstfloor.org>
Date:	Tue,  8 Dec 2009 22:16:22 +0100 (CET)
From:	Andi Kleen <andi@...stfloor.org>
To:	fengguang.wu@...el.com, fengguang.wu@...el.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH] [6/31] HWPOISON: avoid grabbing the page count multiple times during madvise injection


From: Wu Fengguang <fengguang.wu@...el.com>

If page is double referenced in madvise_hwpoison() and __memory_failure(),
remove_mapping() will fail because it expects page_count=2. Fix it by
not grabbing extra page count in __memory_failure().

Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 mm/madvise.c        |    1 -
 mm/memory-failure.c |    8 ++++----
 2 files changed, 4 insertions(+), 5 deletions(-)

Index: linux/mm/madvise.c
===================================================================
--- linux.orig/mm/madvise.c
+++ linux/mm/madvise.c
@@ -238,7 +238,6 @@ static int madvise_hwpoison(unsigned lon
 		       page_to_pfn(p), start);
 		/* Ignore return value for now */
 		__memory_failure(page_to_pfn(p), 0, 1);
-		put_page(p);
 	}
 	return ret;
 }
Index: linux/mm/memory-failure.c
===================================================================
--- linux.orig/mm/memory-failure.c
+++ linux/mm/memory-failure.c
@@ -629,7 +629,7 @@ static void action_result(unsigned long
 }
 
 static int page_action(struct page_state *ps, struct page *p,
-			unsigned long pfn, int ref)
+			unsigned long pfn)
 {
 	int result;
 	int count;
@@ -637,7 +637,7 @@ static int page_action(struct page_state
 	result = ps->action(p, pfn);
 	action_result(pfn, ps->msg, result);
 
-	count = page_count(p) - 1 - ref;
+	count = page_count(p) - 1;
 	if (count != 0)
 		printk(KERN_ERR
 		       "MCE %#lx: %s page still referenced by %d users\n",
@@ -775,7 +775,7 @@ int __memory_failure(unsigned long pfn,
 	 * In fact it's dangerous to directly bump up page count from 0,
 	 * that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
 	 */
-	if (!get_page_unless_zero(compound_head(p))) {
+	if (!ref && !get_page_unless_zero(compound_head(p))) {
 		action_result(pfn, "free or high order kernel", IGNORED);
 		return PageBuddy(compound_head(p)) ? 0 : -EBUSY;
 	}
@@ -823,7 +823,7 @@ int __memory_failure(unsigned long pfn,
 	res = -EBUSY;
 	for (ps = error_states;; ps++) {
 		if (((p->flags | lru_flag)& ps->mask) == ps->res) {
-			res = page_action(ps, p, pfn, ref);
+			res = page_action(ps, p, pfn);
 			break;
 		}
 	}
--
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