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: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/buffer.c b/fs/buffer.c
index 9f69741..891e1c7 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -760,15 +760,9 @@
* 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 @@
}
spin_unlock_irq(&mapping->tree_lock);
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
-
- return 1;
}
/*
@@ -816,6 +808,7 @@
*/
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 @@
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 @@
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);
+ }
}
/*