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?
--- 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.
*/
- Context: Any context except NMI interrupt.
void kvfree(const void *addr) { if (is_vmalloc_addr(addr))
vfree(addr);
vfree_atomic(addr);}