block: Fix overrun in lcm() and move it to lib
lcm() was defined to take integer-sized arguments. The supplied
arguments are multiplied, however, causing us to overflow given
sufficiently large input. That in turn led to incorrect optimal I/O
size reporting in some cases (RAID over RAID).
Switch lcm() over to unsigned long similar to gcd() and move the
function from blk-settings.c to lib.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 31e7a93..4c4700d 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -8,6 +8,7 @@
#include <linux/blkdev.h>
#include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
#include <linux/gcd.h>
+#include <linux/lcm.h>
#include <linux/jiffies.h>
#include "blk.h"
@@ -461,16 +462,6 @@
}
EXPORT_SYMBOL(blk_queue_stack_limits);
-static unsigned int lcm(unsigned int a, unsigned int b)
-{
- if (a && b)
- return (a * b) / gcd(a, b);
- else if (b)
- return b;
-
- return a;
-}
-
/**
* blk_stack_limits - adjust queue_limits for stacked devices
* @t: the stacking driver limits (top device)
diff --git a/include/linux/lcm.h b/include/linux/lcm.h
new file mode 100644
index 0000000..7bf01d7
--- /dev/null
+++ b/include/linux/lcm.h
@@ -0,0 +1,8 @@
+#ifndef _LCM_H
+#define _LCM_H
+
+#include <linux/compiler.h>
+
+unsigned long lcm(unsigned long a, unsigned long b) __attribute_const__;
+
+#endif /* _LCM_H */
diff --git a/lib/Makefile b/lib/Makefile
index 2e152ae..0d40152 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -21,7 +21,7 @@
obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
- string_helpers.o gcd.o list_sort.o
+ string_helpers.o gcd.o lcm.o list_sort.o
ifeq ($(CONFIG_DEBUG_KOBJECT),y)
CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/lcm.c b/lib/lcm.c
new file mode 100644
index 0000000..157cd88
--- /dev/null
+++ b/lib/lcm.c
@@ -0,0 +1,15 @@
+#include <linux/kernel.h>
+#include <linux/gcd.h>
+#include <linux/module.h>
+
+/* Lowest common multiple */
+unsigned long lcm(unsigned long a, unsigned long b)
+{
+ if (a && b)
+ return (a * b) / gcd(a, b);
+ else if (b)
+ return b;
+
+ return a;
+}
+EXPORT_SYMBOL_GPL(lcm);