On Mon, Oct 01, 2012 at 06:26:36PM +0200, Jan Kara wrote: > On s390 any write to a page (even from kernel itself) sets architecture > specific page dirty bit. Thus when a page is written to via standard write, HW > dirty bit gets set and when we later map and unmap the page, > page_remove_rmap() > finds the dirty bit and calls set_page_dirty(). > > Dirtying of a page which shouldn't be dirty can cause all sorts of problems to > filesystems. The bug we observed in practice is that buffers from the page get > freed, so when the page gets later marked as dirty and writeback writes it, > XFS > crashes due to an assertion BUG_ON(!PagePrivate(page)) in page_buffers() > called > from xfs_count_page_state(). > > Similar problem can also happen when zero_user_segment() call from > xfs_vm_writepage() (or block_write_full_page() for that matter) set the > hardware dirty bit during writeback, later buffers get freed, and then page > unmapped. > > Fix the issue by ignoring s390 HW dirty bit for page cache pages in > page_mkclean() and page_remove_rmap(). This is safe because when a page gets > marked as writeable in PTE it is also marked dirty in do_wp_page() or > do_page_fault(). When the dirty bit is cleared by clear_page_dirty_for_io(), > the page gets writeprotected in page_mkclean(). So pagecache page is writeable > if and only if it is dirty. > > CC: Martin Schwidefsky <schwidef...@de.ibm.com> > CC: Mel Gorman <mgor...@suse.de> > CC: linux-s...@vger.kernel.org > Signed-off-by: Jan Kara <j...@suse.cz>
Acked-by: Mel Gorman <mgor...@suse.de> -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
