Quoting Tvrtko Ursulin (2019-07-16 16:25:22) > > On 16/07/2019 13:49, Chris Wilson wrote: > > Following a try_to_unmap() we may want to remove the userptr and so call > > put_pages(). However, try_to_unmap() acquires the page lock and so we > > must avoid recursively locking the pages ourselves -- which means that > > we cannot safely acquire the lock around set_page_dirty(). Since we > > can't be sure of the lock, we have to risk skip dirtying the page, or > > else risk calling set_page_dirty() without a lock and so risk fs > > corruption. > > So if trylock randomly fail we get data corruption in whatever data set > application is working on, which is what the original patch was trying > to avoid? Are we able to detect the backing store type so at least we > don't risk skipping set_page_dirty with anonymous/shmemfs? page->mapping??? We still have the issue that if there is a mapping we should be taking the lock, and we may have both a mapping and be inside try_to_unmap(). I think it's lose-lose. The only way to win is not to userptr :) -Chris
