[PATCH] null_blk: fix spurious IO errors after failed past-wp access

[Alexey Dobriyan <adobriyan@gmail.com>]

Steps to reproduce:

	BLKRESETZONE zone 0

	// force EIO
	pwrite(fd, buf, 4096, 4096);

	[issue more IO including zone ioctls]

It will start failing randomly including IO to unrelated zones because of
->error "reuse". Trigger can be partition detection as well if test is not
run immediately which is even more entertaining.

The fix is of course to clear ->error where necessary.

Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@gmail.com>
---

 drivers/block/null_blk_main.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -605,6 +605,7 @@ static struct nullb_cmd *__alloc_cmd(struct nullb_queue *nq)
 	if (tag != -1U) {
 		cmd = &nq->cmds[tag];
 		cmd->tag = tag;
+		cmd->error = BLK_STS_OK;
 		cmd->nq = nq;
 		if (nq->dev->irqmode == NULL_IRQ_TIMER) {
 			hrtimer_init(&cmd->timer, CLOCK_MONOTONIC,
@@ -1385,6 +1386,7 @@ static blk_status_t null_queue_rq(struct blk_mq_hw_ctx *hctx,
 		cmd->timer.function = null_cmd_timer_expired;
 	}
 	cmd->rq = bd->rq;
+	cmd->error = BLK_STS_OK;
 	cmd->nq = nq;
 
 	blk_mq_start_request(bd->rq);