Messages in this thread | | | Date | Wed, 17 Jun 2020 13:31:57 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive() |
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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
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