Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()

Matthew Wilcox
2020-06-17T11:08:41Z

On Wed, Jun 17, 2020 at 09:12:12AM +0200, Michal Hocko wrote:
> On Tue 16-06-20 17:37:11, Matthew Wilcox wrote:
> > 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.

Actually, it only checks for in_interrupt(). If you call vfree() under
a spinlock, you're in trouble. in_atomic() only knows if we hold a
spinlock for CONFIG_PREEMPT, so it's not safe to check for in_atomic()
in __vfree(). So we need the warning in order that preempt people can
tell those without that there is a bug here.