Hi Andrew,
On 1/27/22 03:53, Andrew Morton wrote:
On Wed, 22 Dec 2021 20:48:28 +0100 Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> 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.
Shakeel proposed to use the approach from Chi.
Decision: https://marc.info/?l=linux-kernel&m=164132032717757&w=2
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.
+ * Context: Any context except NMI interrupt.
*/
void kvfree(const void *addr)
{
if (is_vmalloc_addr(addr))
- vfree(addr);
+ vfree_atomic(addr);
else
kfree(addr);
}
