On Tue 16-06-20 17:37:11, Matthew Wilcox wrote:

On Wed, Jun 17, 2020 at 01:01:30AM +0200, David Sterba wrote:

quoted

On Tue, Jun 16, 2020 at 11:53:50AM -0700, Joe Perches wrote:

quoted

On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote:

quoted

 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@perches.com/ (local)

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