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? -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
