On Wed, Jun 17, 2020 at 09:12:12AM +0200, Michal Hocko wrote:

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

quoted

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.