On Thu, Jan 27, 2022 at 09:25:48AM +0100, Michal Hocko wrote:
On Thu 27-01-22 06:59:50, Manfred Spraul wrote:
Hi Andrew,
On 1/27/22 03:53, Andrew Morton wrote:
On Wed, 22 Dec 2021 20:48:28 +0100 Manfred Spraul manfred@colorfullife.com wrote:
One codepath in find_alloc_undo() calls kvfree() while holding a spinlock. Since vfree() can sleep this is a bug.
Previously, the code path used kfree(), and kfree() is safe to be called while holding a spinlock.
Minghao proposed to fix this by updating find_alloc_undo().
Alternate proposal to fix this: Instead of changing find_alloc_undo(), change kvfree() so that the same rules as for kfree() apply: Having different rules for kfree() and kvfree() just asks for bugs.
Disadvantage: Releasing vmalloc'ed memory will be delayed a bit.
I know we've been around this loop a bunch of times and deferring was considered. But I forget the conclusion. IIRC, mhocko was involved?
I do not remember a mail from mhocko.
I do not remember either.
Shakeel proposed to use the approach from Chi.
Decision: https://marc.info/?l=linux-kernel&m=164132032717757&w=2
And I would agree with Shakeel and go with the original change to the ipc code. That is trivial and without any other side effects like this one. I bet nobody has evaluated what the undconditional deferred freeing has. At least changelog doesn't really dive into that more than a very vague statement that this will happen.
Absolutely agree here. Especially that changing the kvfree() will not look stable.
After applying the https://www.spinics.net/lists/linux-mm/msg282264.html we will be able to use vfree() from atomic anyway.
-- Vlad Rezki