[patch 8/8] mm: __set_page_dirty uses spin_lock_irqsave instead of spin_lock_irq

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From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Subject: mm: __set_page_dirty uses spin_lock_irqsave instead of spin_lock_irq

To use spin_{un}lock_irq is dangerous if caller disabled interrupt. 
During aio buffer migration, we have a possibility to see the following
call stack.

aio_migratepage  [disable interrupt]
  migrate_page_copy
    clear_page_dirty_for_io
      set_page_dirty
        __set_page_dirty_buffers
          __set_page_dirty
            spin_lock_irq

This mean, current aio migration is a deadlockable.  spin_lock_irqsave is
a safer alternative and we should use it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Reported-by: David Rientjes rientjes@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/buffer.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff -puN fs/buffer.c~mm-__set_page_dirty-uses-spin_lock_irqsave-instead-of-spin_lock_irq fs/buffer.c
--- a/fs/buffer.c~mm-__set_page_dirty-uses-spin_lock_irqsave-instead-of-spin_lock_irq
+++ a/fs/buffer.c
@@ -654,14 +654,16 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
 static void __set_page_dirty(struct page *page,
 		struct address_space *mapping, int warn)
 {
-	spin_lock_irq(&mapping->tree_lock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&mapping->tree_lock, flags);
 	if (page->mapping) {	/* Race with truncate? */
 		WARN_ON_ONCE(warn && !PageUptodate(page));
 		account_page_dirtied(page, mapping);
 		radix_tree_tag_set(&mapping->page_tree,
 				page_index(page), PAGECACHE_TAG_DIRTY);
 	}
-	spin_unlock_irq(&mapping->tree_lock);
+	spin_unlock_irqrestore(&mapping->tree_lock, flags);
 	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 }
 
_
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