From a8e7d49aa7be728c4ae241a75a2a124cdcabc0c5 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 19 Mar 2009 11:32:05 -0700 Subject: 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 Signed-off-by: Linus Torvalds --- fs/buffer.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) (limited to 'fs') diff --git a/fs/buffer.c b/fs/buffer.c index 9f697419ed8e..891e1c78e4f1 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -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); + } } /* -- cgit v1.2.3-58-ga151