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.

Cc: <stable@kernel.org>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 1138d1053e9a1a8c9653647e34a70e5ea2e11410..0cc30ecda4c128196cd147fc06f8cf9ddbb1085b 100644 (file)
--- 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)