[PATCH] md_make_request: don"t touch the bio after calling make_request

md_make_request was calling bio_sectors() for part_stat_add
after it was calling the make_request function. This is
bad because the make_request function can free the bio and
because the bi_size field can change around.

The fix here was suggested by Jens Axboe. It saves the
sector count before the make_request call. I hit this
with CONFIG_DEBUG_PAGEALLOC turned on while trying to break
his pretty fusionio card.

Signed-off-by: Chris Mason
---
drivers/md/md.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index b76cfc8..a7d3c3c 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -287,6 +287,7 @@ static int md_make_request(struct request_queue *q, struct bio *bio)
mddev_t *mddev = q->queuedata;
int rv;
int cpu;
+ unsigned int sectors;

if (mddev == NULL || mddev->pers == NULL
|| !mddev->ready) {
@@ -311,12 +312,16 @@ static int md_make_request(struct request_queue *q, struct bio *bio)
atomic_inc(&mddev->active_io);
rcu_read_unlock();

+ /*
+ * save the sectors now since our bio can
+ * go away inside make_request
+ */
+ sectors = bio_sectors(bio);
rv = mddev->pers->make_request(mddev, bio);

cpu = part_stat_lock();
part_stat_inc(cpu, &mddev->gendisk->part0, ios[rw]);
- part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw],
- bio_sectors(bio));
+ part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw], sectors);
part_stat_unlock();

if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
--
1.7.1.1

Re: [PATCH] md_make_request: don"t touch the bio after callingmake_request

On Mon, 07 Feb 2011 14:21:48 -0500 Chris Mason wrote:

> md_make_request was calling bio_sectors() for part_stat_add
> after it was calling the make_request function. This is
> bad because the make_request function can free the bio and
> because the bi_size field can change around.
>
> The fix here was suggested by Jens Axboe. It saves the
> sector count before the make_request call. I hit this
> with CONFIG_DEBUG_PAGEALLOC turned on while trying to break
> his pretty fusionio card.

Thanks Chris!!

I've added it to my queue of md fixes (which I really must send of soon) and
tagged it for -stable.

NeilBrown


>
> Signed-off-by: Chris Mason
> ---
> drivers/md/md.c | 9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index b76cfc8..a7d3c3c 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -287,6 +287,7 @@ static int md_make_request(struct request_queue *q, struct bio *bio)
> mddev_t *mddev = q->queuedata;
> int rv;
> int cpu;
> + unsigned int sectors;
>
> if (mddev == NULL || mddev->pers == NULL
> || !mddev->ready) {
> @@ -311,12 +312,16 @@ static int md_make_request(struct request_queue *q, struct bio *bio)
> atomic_inc(&mddev->active_io);
> rcu_read_unlock();
>
> + /*
> + * save the sectors now since our bio can
> + * go away inside make_request
> + */
> + sectors = bio_sectors(bio);
> rv = mddev->pers->make_request(mddev, bio);
>
> cpu = part_stat_lock();
> part_stat_inc(cpu, &mddev->gendisk->part0, ios[rw]);
> - part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw],
> - bio_sectors(bio));
> + part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw], sectors);
> part_stat_unlock();
>
> if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)