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Commit a8e7d49a authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Fix race in create_empty_buffers() vs __set_page_dirty_buffers() 



Nick Piggin noticed this (very unlikely) race between setting a page
dirty and creating the buffers for it - we need to hold the mapping
private_lock until we've set the page dirty bit in order to make sure
that create_empty_buffers() might not build up a set of buffers without
the dirty bits set when the page is dirty.

I doubt anybody has ever hit this race (and it didn't solve the issue
Nick was looking at), but as Nick says: "Still, it does appear to solve
a real race, which we should close."

Acked-by: default avatarNick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 68df3755

fs/buffer.c

+11 −12
Original line number Diff line number Diff line
@@ -760,15 +760,9 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode); 
 * If warn is true, then emit a warning if the page is not uptodate and has

 * not been truncated.

 */

static int __set_page_dirty(struct page *page,

static void __set_page_dirty(struct page *page,

		struct address_space *mapping, int warn)

{

	if (unlikely(!mapping))

		return !TestSetPageDirty(page);



	if (TestSetPageDirty(page))

		return 0;



	spin_lock_irq(&mapping->tree_lock);

	if (page->mapping) {	/* Race with truncate? */

		WARN_ON_ONCE(warn && !PageUptodate(page));
@@ -785,8 +779,6 @@ static int __set_page_dirty(struct page *page, 
	}

	spin_unlock_irq(&mapping->tree_lock);

	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);



	return 1;

}



/*
@@ -816,6 +808,7 @@ static int __set_page_dirty(struct page *page, 
 */

int __set_page_dirty_buffers(struct page *page)

{

	int newly_dirty;

	struct address_space *mapping = page_mapping(page);



	if (unlikely(!mapping))
@@ -831,9 +824,12 @@ int __set_page_dirty_buffers(struct page *page) 
			bh = bh->b_this_page;

		} while (bh != head);

	}

	newly_dirty = !TestSetPageDirty(page);

	spin_unlock(&mapping->private_lock);



	return __set_page_dirty(page, mapping, 1);

	if (newly_dirty)

		__set_page_dirty(page, mapping, 1);

	return newly_dirty;

}

EXPORT_SYMBOL(__set_page_dirty_buffers);
@@ -1262,8 +1258,11 @@ void mark_buffer_dirty(struct buffer_head *bh) 
			return;

	}



	if (!test_set_buffer_dirty(bh))

		__set_page_dirty(bh->b_page, page_mapping(bh->b_page), 0);

	if (!test_set_buffer_dirty(bh)) {

		struct page *page = bh->b_page;

		if (!TestSetPageDirty(page))

			__set_page_dirty(page, page_mapping(page), 0);

	}

}



/*