On Wed, Mar 17, 2021 at 09:08:28PM -0700, Dan Williams wrote: > Now that device-dax and filesystem-dax are guaranteed to unmap all user > mappings of devmap / DAX pages before tearing down the 'struct page' > array, get_user_pages_fast() can rely on its traditional synchronization > method "validate_pte(); get_page(); revalidate_pte()" to catch races with > device shutdown. Specifically the unmap guarantee ensures that gup-fast > either succeeds in taking a page reference (lock-less), or it detects a > need to fall back to the slow path where the device presence can be > revalidated with locks held. > > Reported-by: Jason Gunthorpe <jgg@xxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > Cc: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> > Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx> > Cc: Dave Jiang <dave.jiang@xxxxxxxxx> > Cc: Ira Weiny <ira.weiny@xxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > mm/gup.c | 38 ++++++++++++++++---------------------- > 1 file changed, 16 insertions(+), 22 deletions(-) I'm happy to see this, and it is really the right thing that PTEs are properly removed before anything happens to the pages under them. Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Jason
