The patch titled
Subject: kfence: move the size check to the beginning of __kfence_alloc()
has been added to the -mm tree. Its filename is
kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch
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------------------------------------------------------
From: Alexander Potapenko <glider@xxxxxxxxxx>
Subject: kfence: move the size check to the beginning of __kfence_alloc()
Check the allocation size before toggling kfence_allocation_gate. This
way allocations that can't be served by KFENCE will not result in waiting
for another CONFIG_KFENCE_SAMPLE_INTERVAL without allocating anything.
Link: https://lkml.kernel.org/r/20210714092222.1890268-1-glider@xxxxxxxxxx
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Suggested-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.12+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kfence/core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/kfence/core.c~kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc
+++ a/mm/kfence/core.c
@@ -734,6 +734,13 @@ void kfence_shutdown_cache(struct kmem_c
void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
{
/*
+ * Perform size check before switching kfence_allocation_gate, so that
+ * we don't disable KFENCE without making an allocation.
+ */
+ if (size > PAGE_SIZE)
+ return NULL;
+
+ /*
* allocation_gate only needs to become non-zero, so it doesn't make
* sense to continue writing to it and pay the associated contention
* cost, in case we have a large number of concurrent allocations.
@@ -757,9 +764,6 @@ void *__kfence_alloc(struct kmem_cache *
if (!READ_ONCE(kfence_enabled))
return NULL;
- if (size > PAGE_SIZE)
- return NULL;
-
return kfence_guarded_alloc(s, size, flags);
}
_
Patches currently in -mm which might be from glider@xxxxxxxxxx are
kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch
kfence-skip-all-gfp_zonemask-allocations.patch
