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 <[email protected]> > Cc: Christoph Hellwig <[email protected]> > Cc: Shiyang Ruan <[email protected]> > Cc: Vishal Verma <[email protected]> > Cc: Dave Jiang <[email protected]> > Cc: Ira Weiny <[email protected]> > Cc: Matthew Wilcox <[email protected]> > Cc: Jan Kara <[email protected]> > Cc: Andrew Morton <[email protected]> > Signed-off-by: Dan Williams <[email protected]> > --- > 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 <[email protected]> Jason
