On Wed 07-12-11 16:49:20, Matthew Wilcox wrote: > On Thu, Dec 08, 2011 at 12:16:58AM +0100, Jan Kara wrote: > > On Tue 06-12-11 06:35:44, Christoph Hellwig wrote: > > > We make sure to not dirty any new inodes after the first phase of the > > > freeze, so this should be a BUG_ON/WARN_ON. > > This is not really true in presence of mmaped writes. To block mmaped > > writes on a frozen filesystem, we need some synchronization between > > page_mkwrite() and freezing code. Currently, to avoid any additional > > locking overhead, we set page dirty and *then* check for filesystem being > > frozen. Only this order can make sure either the page is written (and > > write-protected) or the frozen check triggers and we wait... (see the > > comment in block_page_mkwrite()). The nasty sideeffect of this is that > > there can be dirty pages & inodes on a frozen filesystem. We are blocked in > > the page fault of these pages so user cannot write any data to these pages > > but still they are marked dirty. > > Can't we make the mmaps read-only during the freezing process? But then application will get EFAULT instead of blocking? I don't think that is acceptable (we'd see lots of applications dying ;). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
