null_blk: fix use-after-free error
null_blk: fix use-after-free error

blk_end_request_all may free request, so we need to save
request_queue pointer before blk_end_request_all call.

The problem was introduced in commit cf8ecc5a8455266f8d51
("null_blk: guarantee device restart in all irq modes")
and causes general protection fault with slab poisoning
enabled.

Fixes: cf8ecc5a8455266f8d51 ("null_blk: guarantee device
       restart in all irq modes")

Signed-off-by: Mike Krinkin <9a024e2544da0dd1d651d8a76b83357108d77e55@gmail.com>
Reviewed-by: Ming Lei <572efd9047f12626ad5bcb995a452788646858f3@gmail.com>
Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@fb.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs