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Commit 2cda2728 authored by Martin K. Petersen's avatar Martin K. Petersen Committed by Jens Axboe
Browse files

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: default avatarMartin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent f11c9c5c

block/blk-settings.c

+1 −10
Original line number Diff line number Diff line
@@ -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 @@ void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b) 
}

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)

include/linux/lcm.h

0 → 100644
+8 −0
Original line number Diff line number Diff line 
#ifndef _LCM_H

#define _LCM_H



#include <linux/compiler.h>



unsigned long lcm(unsigned long a, unsigned long b) __attribute_const__;



#endif /* _LCM_H */

lib/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ lib-y += kobject.o kref.o klist.o 


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

lib/lcm.c

0 → 100644
+15 −0
Original line number Diff line number Diff line 
#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);