* [PATCH] block:Remove extra condition in end of disk check
@ 2013-06-23 17:17 Raghavendra K T
2013-06-24 13:50 ` Raghavendra K T
0 siblings, 1 reply; 4+ messages in thread
From: Raghavendra K T @ 2013-06-23 17:17 UTC (permalink / raw)
To: Jens Axboe, LKML; +Cc: raghavendra.kt
From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Since #sector is always positive the reduced condition check
encompasses maxsector < nr_sectors check.
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
---
An userspace program looping with:
maxsector - 0-9999
nr_sector - 0-999
sector - 0-999 gave 6.4% improvement with new condition though I agree that
it is not the best way to test it perhaps :)
diff --git a/block/blk-core.c b/block/blk-core.c
index 33c33bc..4a78583 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1656,7 +1656,7 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
if (maxsector) {
sector_t sector = bio->bi_sector;
- if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
+ if (maxsector - nr_sectors < sector) {
/*
* This may well happen - the kernel calls bread()
* without checking the size of the device, e.g., when
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] block:Remove extra condition in end of disk check
2013-06-23 17:17 [PATCH] block:Remove extra condition in end of disk check Raghavendra K T
@ 2013-06-24 13:50 ` Raghavendra K T
2013-06-24 22:51 ` Tejun Heo
0 siblings, 1 reply; 4+ messages in thread
From: Raghavendra K T @ 2013-06-24 13:50 UTC (permalink / raw)
To: LKML, Tejun Heo, Andrew Morton
Cc: Raghavendra K T, Jens Axboe, Kiyoshi Ueda, Lin Ming, Christoph Hellwig
CCing more relevant people (with the help of get_maintainer --git-blame)
On 06/23/2013 10:47 PM, Raghavendra K T wrote:
> From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
>
> Since #sector is always positive the reduced condition check
> encompasses maxsector < nr_sectors check.
>
> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
> ---
> An userspace program looping with:
> maxsector - 0-9999
> nr_sector - 0-999
> sector - 0-999 gave 6.4% improvement with new condition though I agree that
> it is not the best way to test it perhaps :)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 33c33bc..4a78583 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1656,7 +1656,7 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
> if (maxsector) {
> sector_t sector = bio->bi_sector;
>
> - if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
> + if (maxsector - nr_sectors < sector) {
> /*
> * This may well happen - the kernel calls bread()
> * without checking the size of the device, e.g., when
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block:Remove extra condition in end of disk check
2013-06-24 13:50 ` Raghavendra K T
@ 2013-06-24 22:51 ` Tejun Heo
2013-06-25 5:10 ` Raghavendra K T
0 siblings, 1 reply; 4+ messages in thread
From: Tejun Heo @ 2013-06-24 22:51 UTC (permalink / raw)
To: Raghavendra K T
Cc: LKML, Andrew Morton, Jens Axboe, Kiyoshi Ueda, Lin Ming,
Christoph Hellwig
On Mon, Jun 24, 2013 at 07:20:12PM +0530, Raghavendra K T wrote:
> >@@ -1656,7 +1656,7 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
> > if (maxsector) {
> > sector_t sector = bio->bi_sector;
> >
> >- if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
> >+ if (maxsector - nr_sectors < sector) {
If maxsector < nr_sectors, the subtraction will underflow making it a
very large number and fail to detect the invalid condition, no?
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block:Remove extra condition in end of disk check
2013-06-24 22:51 ` Tejun Heo
@ 2013-06-25 5:10 ` Raghavendra K T
0 siblings, 0 replies; 4+ messages in thread
From: Raghavendra K T @ 2013-06-25 5:10 UTC (permalink / raw)
To: Tejun Heo
Cc: LKML, Andrew Morton, Jens Axboe, Kiyoshi Ueda, Lin Ming,
Christoph Hellwig
On 06/25/2013 04:21 AM, Tejun Heo wrote:
> On Mon, Jun 24, 2013 at 07:20:12PM +0530, Raghavendra K T wrote:
>>> @@ -1656,7 +1656,7 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
>>> if (maxsector) {
>>> sector_t sector = bio->bi_sector;
>>>
>>> - if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
>>> + if (maxsector - nr_sectors < sector) {
>
> If maxsector < nr_sectors, the subtraction will underflow making it a
> very large number and fail to detect the invalid condition, no?
>
Hi Tejun,
Thanks for the reply and explanation. You are right. underflow results
in invalid condition.
Considering maxsector and sectors are unsigned long, and nr_sector is
unsigned int, probably safer bet is
(max_sector < sector + nr_sector), but still it would leave scope for
overflow.
Thanks again,
Raghu.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2013-06-23 17:17 [PATCH] block:Remove extra condition in end of disk check Raghavendra K T
2013-06-24 13:50 ` Raghavendra K T
2013-06-24 22:51 ` Tejun Heo
2013-06-25 5:10 ` Raghavendra K T
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