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.
With Reviewed-by:
https://marc.info/?l=linux-kernel&m=164132744522325&w=2
--- a/mm/util.c +++ b/mm/util.c @@ -610,12 +610,12 @@ EXPORT_SYMBOL(kvmalloc_node);
- It is slightly more efficient to use kfree() or vfree() if you are certain
- that you know which one to use.
- Context: Either preemptible task context or not-NMI interrupt.
*/ void kvfree(const void *addr) { if (is_vmalloc_addr(addr))
- Context: Any context except NMI interrupt.
vfree(addr);
vfree_atomic(addr);