[04/15] kfence: move the size check to the beginning of __kfence_alloc()

Commit Message

Andrew Morton July 23, 2021, 10:50 p.m. UTC

From: Alexander Potapenko <[e-mail]>
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/[e-mail]
Signed-off-by: Alexander Potapenko <[e-mail]>
Suggested-by: Marco Elver <[e-mail]>
Reviewed-by: Marco Elver <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: <[e-mail]>	[5.12+]
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/kfence/core.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Patch

--- 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);
 }