3.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: KOSAKI Motohiro <kosaki.motoh...@jp.fujitsu.com>

commit 227d53b397a32a7614667b3ecaf1d89902fb6c12 upstream.

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.motoh...@jp.fujitsu.com>
Reported-by: David Rientjes rient...@google.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

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

--- a/fs/buffer.c
+++ b/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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