On Thu, 11 Oct 2012 08:56:00 +1100 Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Tue, Oct 09, 2012 at 07:19:09PM -0700, Hugh Dickins wrote: > > On Tue, 9 Oct 2012, Jan Kara wrote: > > > On Mon 08-10-12 21:24:40, Hugh Dickins wrote: > > > > On Mon, 1 Oct 2012, 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(). > > > > > > > > What changed recently? Was XFS hardly used on s390 until now? > > > The problem was originally hit on SLE11-SP2 which is 3.0 based after > > > migration of our s390 build machines from SLE11-SP1 (2.6.32 based). I think > > > XFS just started to be more peevish about what pages it gets between these > > > two releases ;) (e.g. ext3 or ext4 just says "oh, well" and fixes things > > > up). > > > > Right, in 2.6.32 xfs_vm_writepage() had a !page_has_buffers(page) case, > > whereas by 3.0 that had become ASSERT(page_has_buffers(page)), with the > > ASSERT usually compiled out, stumbling later in page_buffers() as you say. > > What that says is that no-one is running xfstests-based QA on s390 > with CONFIG_XFS_DEBUG enabled, otherwise this would have been found. > I've never tested XFS on s390 before, and I doubt any of the > upstream developers have, either, because not many peopl ehave s390 > machines in their basement. So this is probably just an oversight > in the distro QA environment more than anything.... Our internal builds indeed have CONFIG_XFS_DEBUG=n, I'll change that and watch for the fallout. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>