On Sat, Nov 25, 2017 at 10:35:43PM +0000, David Howells wrote: > Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > So I see in the commit message why afs needs to do this, but it's > > worth pointing out that it's > > > > (a) impossible to avoid the "inconsistent data" case for writable mmap'ed > > pages > > Doesn't clear_page_dirty_for_io() write-protect the PTE for the page to be > written out, in which case ->page_mkwrite() will get called again before the > page is redirtied? Yes, but page_mkwrite will only block on writeback in progress is if the backing device says it needs stable pages. See wait_for_stable_page(). e.g. stable pages are required if RAID is in use, otherwise modification during IO can result in broken on-disk parity/mirroring.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
