On Thu, Aug 23, 2012 at 05:11:25PM +0800, Fengguang Wu wrote:

On Wed, Aug 22, 2012 at 11:17:35AM -0400, Naoya Horiguchi wrote:

quoted

"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.

Good point!
 

quoted

Signed-off-by: Naoya Horiguchi <redacted>
---
 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;
+		}

That chunk prevents reclaiming all the cached pages. However the intention
is only to keep the struct inode together with the hwpoison bit?

Yes, we can not reclaim pagecaches from shrink_slab(), but we can do from
shrink_zone(). So it shouldn't happen that cached pages on hwpoisoned file
remain for long under high memory pressure.

quoted

+		/*
 		 * 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);

Is that clear necessary? Because the bit will be gone with the inode
struct: it's going to be de-allocated anyway.

With the chunk in prune_icache_sb() we keep the inode struct with
AS_HWPOISON set on memory, so in order to remove it, we need explicitly
clear the bit.
Without this clear, the inode remains until system reboot.

quoted

 	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))

It might be a bit better to test !newsize first.

Ah, OK.

Thanks,
Naoya

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>