From 8e9d78edea3ce5c0036f85b93091483f2f15443a Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 21 Aug 2009 17:40:08 -0700 Subject: [PATCH] Re-introduce page mapping check in mark_buffer_dirty() In commit a8e7d49aa7be728c4ae241a75a2a124cdcabc0c5 ("Fix race in create_empty_buffers() vs __set_page_dirty_buffers()"), I removed a test for a NULL page mapping unintentionally when some of the code inside __set_page_dirty() was moved to the callers. That removal generally didn't matter, since a filesystem would serialize truncation (which clears the page mapping) against writing (which marks the buffer dirty), so locking at a higher level (either per-page or an inode at a time) should mean that the buffer page would be stable. And indeed, nothing bad seemed to happen. Except it turns out that apparently reiserfs does something odd when under load and writing out the journal, and we have a number of bugzilla entries that look similar: http://bugzilla.kernel.org/show_bug.cgi?id=13556 http://bugzilla.kernel.org/show_bug.cgi?id=13756 http://bugzilla.kernel.org/show_bug.cgi?id=13876 and it looks like reiserfs depended on that check (the common theme seems to be "data=journal", and a journal writeback during a truncate). I suspect reiserfs should have some additional locking, but in the meantime this should get us back to the pre-2.6.29 behavior. Pattern-pointed-out-by: Roland Kletzing Cc: stable@kernel.org (2.6.29 and 2.6.30) Cc: Jeff Mahoney Cc: Nick Piggin Cc: Al Viro Signed-off-by: Linus Torvalds --- fs/buffer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/buffer.c b/fs/buffer.c index a3ef091..28f320f 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1165,8 +1165,11 @@ void mark_buffer_dirty(struct buffer_head *bh) if (!test_set_buffer_dirty(bh)) { struct page *page = bh->b_page; - if (!TestSetPageDirty(page)) - __set_page_dirty(page, page_mapping(page), 0); + if (!TestSetPageDirty(page)) { + struct address_space *mapping = page_mapping(page); + if (mapping) + __set_page_dirty(page, mapping, 0); + } } } -- 2.7.4