[PATCH] [8/31] HWPOISON: abort on failed unmap

[Andi Kleen <andi@firstfloor.org>]

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

Don't try to isolate a still mapped page. Otherwise we will hit the
BUG_ON(page_mapped(page)) in __remove_from_page_cache().

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

---
 mm/memory-failure.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

Index: linux/mm/memory-failure.c
===================================================================
--- linux.orig/mm/memory-failure.c
+++ linux/mm/memory-failure.c
@@ -657,7 +657,7 @@ static int page_action(struct page_state
  * Do all that is necessary to remove user space mappings. Unmap
  * the pages and send SIGBUS to the processes if the data was dirty.
  */
-static void hwpoison_user_mappings(struct page *p, unsigned long pfn,
+static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 				  int trapno)
 {
 	enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
@@ -667,15 +667,18 @@ static void hwpoison_user_mappings(struc
 	int i;
 	int kill = 1;
 
-	if (PageReserved(p) || PageCompound(p) || PageSlab(p) || PageKsm(p))
-		return;
+	if (PageReserved(p) || PageSlab(p))
+		return SWAP_SUCCESS;
 
 	/*
 	 * This check implies we don't kill processes if their pages
 	 * are in the swap cache early. Those are always late kills.
 	 */
 	if (!page_mapped(p))
-		return;
+		return SWAP_SUCCESS;
+
+	if (PageCompound(p) || PageKsm(p))
+		return SWAP_FAIL;
 
 	if (PageSwapCache(p)) {
 		printk(KERN_ERR
@@ -737,6 +740,8 @@ static void hwpoison_user_mappings(struc
 	 */
 	kill_procs_ao(&tokill, !!PageDirty(p), trapno,
 		      ret != SWAP_SUCCESS, pfn);
+
+	return ret;
 }
 
 int __memory_failure(unsigned long pfn, int trapno, int flags)
@@ -809,8 +814,13 @@ int __memory_failure(unsigned long pfn,
 
 	/*
 	 * Now take care of user space mappings.
+	 * Abort on fail: __remove_from_page_cache() assumes unmapped page.
 	 */
-	hwpoison_user_mappings(p, pfn, trapno);
+	if (hwpoison_user_mappings(p, pfn, trapno) != SWAP_SUCCESS) {
+		printk(KERN_ERR "MCE %#lx: cannot unmap page, give up\n", pfn);
+		res = -EBUSY;
+		goto out;
+	}
 
 	/*
 	 * Torn down by someone else?

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