[PATCH] AB-BA deadlock in drop_caches sysctl (resend, the one sent was for 2.6.18)

["Denis V. Lunev" <den@openvz.org>]

There is a AB-BA deadlock regarding drop_caches sysctl. Here are the code
paths:

drop_pagecache
  spin_lock(&inode_lock);
  invalidate_mapping_pages
    try_to_release_page
      ext3_releasepage
        journal_try_to_free_buffers
          __journal_try_to_free_buffer
	    spin_lock(&journal->j_list_lock);

__journal_temp_unlink_buffer (called under journal->j_list_lock by comments)
  mark_buffer_dirty
    __set_page_dirty
      __mark_inode_dirty
        spin_lock(&inode_lock);

The patch tries to address the issue - it drops inode_lock before digging into
invalidate_inode_pages. This seems sane as inode hold should not gone from the
list and should not change its place.

Signed-off-by: Denis V. Lunev <den@openvz.org>
--
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 59375ef..4ac80d8 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -14,15 +14,27 @@ int sysctl_drop_caches;
 
 static void drop_pagecache_sb(struct super_block *sb)
 {
-	struct inode *inode;
+	struct inode *inode, *old;
 
+	old = NULL;
 	spin_lock(&inode_lock);
 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
 		if (inode->i_state & (I_FREEING|I_WILL_FREE))
 			continue;
-		__invalidate_mapping_pages(inode->i_mapping, 0, -1, true);
+		__iget(inode);
+		spin_unlock(&inode_lock);
+
+		if (old != NULL)
+			iput(old);
+		invalidate_mapping_pages(inode->i_mapping, 0, -1);
+		old = inode;
+
+		spin_lock(&inode_lock);
 	}
 	spin_unlock(&inode_lock);
+
+	if (old != NULL)
+		iput(old);
 }
 
 void drop_pagecache(void)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b3ec4a4..b424dff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1649,9 +1649,6 @@ extern int __invalidate_device(struct block_device *);
 extern int invalidate_partition(struct gendisk *, int);
 #endif
 extern int invalidate_inodes(struct super_block *);
-unsigned long __invalidate_mapping_pages(struct address_space *mapping,
-					pgoff_t start, pgoff_t end,
-					bool be_atomic);
 unsigned long invalidate_mapping_pages(struct address_space *mapping,
 					pgoff_t start, pgoff_t end);
 
diff --git a/mm/truncate.c b/mm/truncate.c
index cadc156..5cbe1e7 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -266,8 +266,21 @@ void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
 }
 EXPORT_SYMBOL(truncate_inode_pages);
 
-unsigned long __invalidate_mapping_pages(struct address_space *mapping,
-				pgoff_t start, pgoff_t end, bool be_atomic)
+/**
+ * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
+ * @mapping: the address_space which holds the pages to invalidate
+ * @start: the offset 'from' which to invalidate
+ * @end: the offset 'to' which to invalidate (inclusive)
+ *
+ * This function only removes the unlocked pages, if you want to
+ * remove all the pages of one inode, you must call truncate_inode_pages.
+ *
+ * invalidate_mapping_pages() will not block on IO activity. It will not
+ * invalidate pages which are dirty, locked, under writeback or mapped into
+ * pagetables.
+ */
+unsigned long invalidate_mapping_pages(struct address_space *mapping,
+				pgoff_t start, pgoff_t end)
 {
 	struct pagevec pvec;
 	pgoff_t next = start;
@@ -308,30 +321,10 @@ unlock:
 				break;
 		}
 		pagevec_release(&pvec);
-		if (likely(!be_atomic))
-			cond_resched();
+		cond_resched();
 	}
 	return ret;
 }
-
-/**
- * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
- * @mapping: the address_space which holds the pages to invalidate
- * @start: the offset 'from' which to invalidate
- * @end: the offset 'to' which to invalidate (inclusive)
- *
- * This function only removes the unlocked pages, if you want to
- * remove all the pages of one inode, you must call truncate_inode_pages.
- *
- * invalidate_mapping_pages() will not block on IO activity. It will not
- * invalidate pages which are dirty, locked, under writeback or mapped into
- * pagetables.
- */
-unsigned long invalidate_mapping_pages(struct address_space *mapping,
-				pgoff_t start, pgoff_t end)
-{
-	return __invalidate_mapping_pages(mapping, start, end, false);
-}
 EXPORT_SYMBOL(invalidate_mapping_pages);
 
 /*