On Tue 16-06-20 17:37:11, Matthew Wilcox wrote: > On Wed, Jun 17, 2020 at 01:01:30AM +0200, David Sterba wrote: > > On Tue, Jun 16, 2020 at 11:53:50AM -0700, Joe Perches wrote: > > > On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote: > > > > v4: > > > > - Break out the memzero_explicit() change as suggested by Dan Carpenter > > > > so that it can be backported to stable. > > > > - Drop the "crypto: Remove unnecessary memzero_explicit()" patch for > > > > now as there can be a bit more discussion on what is best. It will be > > > > introduced as a separate patch later on after this one is merged. > > > > > > To this larger audience and last week without reply: > > > https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@xxxxxxxxxxx/ > > > > > > Are there _any_ fastpath uses of kfree or vfree? > > > > I'd consider kfree performance critical for cases where it is called > > under locks. If possible the kfree is moved outside of the critical > > section, but we have rbtrees or lists that get deleted under locks and > > restructuring the code to do eg. splice and free it outside of the lock > > is not always possible. > > Not just performance critical, but correctness critical. Since kvfree() > may allocate from the vmalloc allocator, I really think that kvfree() > should assert that it's !in_atomic(). Otherwise we can get into trouble > if we end up calling vfree() and have to take the mutex. FWIW __vfree already checks for atomic context and put the work into a deferred context. So this should be safe. It should be used as a last resort, though. -- Michal Hocko SUSE Labs
