Commit 9a19aeb5 authored by Marco Elver's avatar Marco Elver Committed by Linus Torvalds
Browse files

kfence: count unexpectedly skipped allocations 

Maintain a counter to count allocations that are skipped due to being
incompatible (oversized, incompatible gfp flags) or no capacity.

This is to compute the fraction of allocations that could not be
serviced by KFENCE, which we expect to be rare.

Link: https://lkml.kernel.org/r/20210923104803.2620285-2-elver@google.com


Signed-off-by: default avatarMarco Elver <elver@google.com>
Reviewed-by: default avatarDmitry Vyukov <dvyukov@google.com>
Acked-by: default avatarAlexander Potapenko <glider@google.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Taras Madan <tarasmadan@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f39f21b3

mm/kfence/core.c

+13 −3
Original line number Diff line number Diff line
@@ -112,6 +112,8 @@ enum kfence_counter_id { 
	KFENCE_COUNTER_FREES,

	KFENCE_COUNTER_ZOMBIES,

	KFENCE_COUNTER_BUGS,

	KFENCE_COUNTER_SKIP_INCOMPAT,

	KFENCE_COUNTER_SKIP_CAPACITY,

	KFENCE_COUNTER_COUNT,

};

static atomic_long_t counters[KFENCE_COUNTER_COUNT];
@@ -121,6 +123,8 @@ static const char *const counter_names[] = { 
	[KFENCE_COUNTER_FREES]		= "total frees",

	[KFENCE_COUNTER_ZOMBIES]	= "zombie allocations",

	[KFENCE_COUNTER_BUGS]		= "total bugs",

	[KFENCE_COUNTER_SKIP_INCOMPAT]	= "skipped allocations (incompatible)",

	[KFENCE_COUNTER_SKIP_CAPACITY]	= "skipped allocations (capacity)",

};

static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT);
@@ -271,8 +275,10 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g 
		list_del_init(&meta->list);

	}

	raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);

	if (!meta)

	if (!meta) {

		atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_CAPACITY]);

		return NULL;

	}



	if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) {

		/*
@@ -740,8 +746,10 @@ 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)

	if (size > PAGE_SIZE) {

		atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]);

		return NULL;

	}



	/*

	 * Skip allocations from non-default zones, including DMA. We cannot
@@ -749,8 +757,10 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) 
	 * properties (e.g. reside in DMAable memory).

	 */

	if ((flags & GFP_ZONEMASK) ||

	    (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))

	    (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) {

		atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]);

		return NULL;

	}



	/*

	 * allocation_gate only needs to become non-zero, so it doesn't make