block: blk_init_allocated_queue() set q->fq as NULL in the fail case

We find the memory use-after-free issue in __blk_drain_queue()
on the kernel 4.14. After read the latest kernel 4.18-rc6 we
think it has the same problem.

Memory is allocated for q->fq in the blk_init_allocated_queue().
If the elevator init function called with error return, it will
run into the fail case to free the q->fq.

Then the __blk_drain_queue() uses the same memory after the free
of the q->fq, it will lead to the unpredictable event.

The patch is to set q->fq as NULL in the fail case of
blk_init_allocated_queue().

Fixes: commit 7c94e1c157a2 ("block: introduce blk_flush_queue to drive flush machinery")
Cc: <stable@vger.kernel.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: xiao jin <jin.xiao@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
blk_qc_t submit_bio(struct bio *bio)
{
	/*
	 * If it's a regular read/write or a barrier with data attached,
	 * go through the normal accounting stuff before submission.
	 */
	if (bio_has_data(bio)) {
		unsigned int count;

		if (unlikely(bio_op(bio) == REQ_OP_WRITE_SAME))
			count = queue_logical_block_size(bio->bi_disk->queue) >> 9;
		else
			count = bio_sectors(bio);

		if (op_is_write(bio_op(bio))) {
			count_vm_events(PGPGOUT, count);
		} else {
			task_io_account_read(bio->bi_iter.bi_size);
			count_vm_events(PGPGIN, count);
		}

		if (unlikely(block_dump)) {
			char b[BDEVNAME_SIZE];
			printk(KERN_DEBUG "%s(%d): %s block %Lu on %s (%u sectors)\n",
			current->comm, task_pid_nr(current),
				op_is_write(bio_op(bio)) ? "WRITE" : "READ",
				(unsigned long long)bio->bi_iter.bi_sector,
				bio_devname(bio, b), count);
		}
	}

	return generic_make_request(bio);
}

blk_qc_t submit_bio(struct bio *bio)
{
	/*
	 * If it's a regular read/write or a barrier with data attached,
	 * go through the normal accounting stuff before submission.
	 */
	if (bio_has_data(bio)) {
		unsigned int count;

		if (unlikely(bio_op(bio) == REQ_OP_WRITE_SAME))
			count = queue_logical_block_size(bio->bi_disk->queue) >> 9;
		else
			count = bio_sectors(bio);

		if (op_is_write(bio_op(bio))) {
			count_vm_events(PGPGOUT, count);
		} else {
			task_io_account_read(bio->bi_iter.bi_size);
			count_vm_events(PGPGIN, count);
		}

		if (unlikely(block_dump)) {
			char b[BDEVNAME_SIZE];
			printk(KERN_DEBUG "%s(%d): %s block %Lu on %s (%u sectors)\n",
			current->comm, task_pid_nr(current),
				op_is_write(bio_op(bio)) ? "WRITE" : "READ",
				(unsigned long long)bio->bi_iter.bi_sector,
				bio_devname(bio, b), count);
		}
	}

	return generic_make_request(bio);
}
