From: zijun_hu <zijun_hu@xxxxxxx>
the percpu allocator only works well currently when allocates a power of
2 aligned area, but there aren't any hints for alignment requirement, so
memory leakage maybe be caused if allocate other alignment areas
the alignment must be a even at least since the LSB of a chunk->map element
is used as free/in-use flag of a area; besides, the alignment must be a
power of 2 too since ALIGN() doesn't work well for other alignment always
but is adopted by pcpu_fit_in_area(). IOW, the current allocator only works
well for a power of 2 aligned area allocation.
see below opposite example for why a odd alignment doesn't work
lets assume area [16, 36) is free but its previous one is in-use, we want
to allocate a @size == 8 and @align == 7 area. the larger area [16, 36) is
split to three areas [16, 21), [21, 29), [29, 36) eventually. however, due
to the usage for a chunk->map element, the actual offset of the aim area
[21, 29) is 21 but is recorded in relevant element as 20; moreover the
residual tail free area [29, 36) is mistook as in-use and is lost silently
unlike macro roundup(), ALIGN(x, a) doesn't work if @a isn't a power of 2
for example, roundup(10, 6) == 12 but ALIGN(10, 6) == 10, and the latter
result isn't desired obviously.
fix it by appending sanity checkup for alignment requirement
Signed-off-by: zijun_hu <zijun_hu@xxxxxxx>
Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
---
include/linux/kernel.h | 1 +
mm/percpu.c | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index bc6ed52a39b9..0dc0b21bd164 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -45,6 +45,7 @@
#define REPEAT_BYTE(x) ((~0ul / 0xff) * (x))
+/* @a is a power of 2 value */
#define ALIGN(x, a) __ALIGN_KERNEL((x), (a))
#define __ALIGN_MASK(x, mask) __ALIGN_KERNEL_MASK((x), (mask))
#define PTR_ALIGN(p, a) ((typeof(p))ALIGN((unsigned long)(p), (a)))
diff --git a/mm/percpu.c b/mm/percpu.c
index 255714302394..10ba3f9a3826 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -886,7 +886,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
size = ALIGN(size, 2);
- if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
+ if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE
+ || !is_power_of_2(align))) {
WARN(true, "illegal size (%zu) or align (%zu) for percpu allocation\n",
size, align);
return NULL;
--
1.9.1
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>