On Wed 17-06-20 04:08:20, Matthew Wilcox wrote: > 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(). You are right. I have misremembered. You have made me look (thanks) ... > 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. ... Unless I am missing something in_interrupt depends on preempt_count() as well so neither of the two is reliable without PREEMPT_COUNT configured. -- Michal Hocko SUSE Labs
