[PATCH 3/3] HWPOISON: prevent inode cache removal to keep AS_HWPOISON sticky

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

"HWPOISON: report sticky EIO for poisoned file" still has a corner case
where we have possibilities of data lost. This is because in this fix
AS_HWPOISON is cleared when the inode cache is dropped.

For example, consider an application in which a process periodically
(every 10 minutes) writes some logs on a file (and closes it after
each writes,) and at the end of each day some batch programs run using
the log file. If a memory error hits on dirty pagecache of this log file
just after periodic write/close and the inode cache is cleared before the
next write, then this application is not aware of the error and the batch
programs will work wrongly.

To avoid this, this patch makes us pin the hwpoisoned inode on memory
until we remove or completely truncate the hwpoisoned file.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 fs/inode.c              | 12 ++++++++++++
 include/linux/pagemap.h | 11 +++++++++++
 mm/memory-failure.c     |  2 +-
 mm/truncate.c           |  2 ++
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git v3.6-rc1.orig/fs/inode.c v3.6-rc1/fs/inode.c
index ac8d904..8742397 100644
--- v3.6-rc1.orig/fs/inode.c
+++ v3.6-rc1/fs/inode.c
@@ -717,6 +717,15 @@ void prune_icache_sb(struct super_block *sb, int nr_to_scan)
 		}
 
 		/*
+		 * Keep inode caches on memory for user processes to certainly
+		 * be aware of memory errors.
+		 */
+		if (unlikely(mapping_hwpoison(inode->i_mapping))) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+
+		/*
 		 * Referenced or dirty inodes are still in use. Give them
 		 * another pass through the LRU as we canot reclaim them now.
 		 */
@@ -1405,6 +1414,9 @@ static void iput_final(struct inode *inode)
 		inode->i_state &= ~I_WILL_FREE;
 	}
 
+	if (unlikely(mapping_hwpoison(inode->i_mapping) && drop))
+		mapping_clear_hwpoison(inode->i_mapping);
+
 	inode->i_state |= I_FREEING;
 	if (!list_empty(&inode->i_lru))
 		inode_lru_list_del(inode);
diff --git v3.6-rc1.orig/include/linux/pagemap.h v3.6-rc1/include/linux/pagemap.h
index 4d8d821..9fce4e4 100644
--- v3.6-rc1.orig/include/linux/pagemap.h
+++ v3.6-rc1/include/linux/pagemap.h
@@ -59,11 +59,22 @@ static inline int mapping_hwpoison(struct address_space *mapping)
 {
 	return test_bit(AS_HWPOISON, &mapping->flags);
 }
+static inline void mapping_set_hwpoison(struct address_space *mapping)
+{
+	set_bit(AS_HWPOISON, &mapping->flags);
+}
+static inline void mapping_clear_hwpoison(struct address_space *mapping)
+{
+	clear_bit(AS_HWPOISON, &mapping->flags);
+}
 #else
 static inline int mapping_hwpoison(struct address_space *mapping)
 {
 	return 0;
 }
+static inline void mapping_clear_hwpoison(struct address_space *mapping)
+{
+}
 #endif
 
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
diff --git v3.6-rc1.orig/mm/memory-failure.c v3.6-rc1/mm/memory-failure.c
index a1e7e00..ca064c6 100644
--- v3.6-rc1.orig/mm/memory-failure.c
+++ v3.6-rc1/mm/memory-failure.c
@@ -652,7 +652,7 @@ static int me_pagecache_dirty(struct page *p, unsigned long pfn)
 		 * the first EIO, but we're not worse than other parts
 		 * of the kernel.
 		 */
-		set_bit(AS_HWPOISON, &mapping->flags);
+		mapping_set_hwpoison(mapping);
 	}
 
 	return me_pagecache_clean(p, pfn);
diff --git v3.6-rc1.orig/mm/truncate.c v3.6-rc1/mm/truncate.c
index 75801ac..82a994f 100644
--- v3.6-rc1.orig/mm/truncate.c
+++ v3.6-rc1/mm/truncate.c
@@ -574,6 +574,8 @@ void truncate_setsize(struct inode *inode, loff_t newsize)
 
 	oldsize = inode->i_size;
 	i_size_write(inode, newsize);
+	if (unlikely(mapping_hwpoison(inode->i_mapping) && !newsize))
+		mapping_clear_hwpoison(inode->i_mapping);
 
 	truncate_pagecache(inode, oldsize, newsize);
 }
-- 
1.7.11.4

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