md/raid5: protect debug message against NULL derefernce.

The pr_debug in add_stripe_bio could race with something
changing *bip, so it is best to hold the lock until
after the pr_debug.

Reported-by: "Jianpeng Ma" <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 36c0a15..d110126 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2436,11 +2436,11 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
                if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
                        set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
        }
-       spin_unlock_irq(&sh->stripe_lock);
 
        pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
                (unsigned long long)(*bip)->bi_sector,
                (unsigned long long)sh->sector, dd_idx);
+       spin_unlock_irq(&sh->stripe_lock);
 
        if (conf->mddev->bitmap && firstwrite) {
                bitmap_startwrite(conf->mddev->bitmap, sh->sector,