null_blk: add blocking mode

This adds a new module parameter to null_blk, blocking. If set, null_blk
will set the BLK_MQ_F_BLOCKING flag, indicating that it sometimes/always
needs to block in its ->queue_rq() function.  The intent is to help find
regressions in blocking drivers, since not many of them exist.

If null_blk is loaded with submit_queues > 1 and blocking=1, this
shows the regression recently fixed by bf4907c05e61.

Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 6f2e565..444f8d8 100644 (file)
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -117,6 +117,10 @@ static bool use_lightnvm;
 module_param(use_lightnvm, bool, S_IRUGO);
 MODULE_PARM_DESC(use_lightnvm, "Register as a LightNVM device");
 
+static bool blocking;
+module_param(blocking, bool, S_IRUGO);
+MODULE_PARM_DESC(blocking, "Register as a blocking blk-mq driver device");
+
 static int irqmode = NULL_IRQ_SOFTIRQ;
 
 static int null_set_irqmode(const char *str, const struct kernel_param *kp)
@@ -357,6 +361,8 @@ static int null_queue_rq(struct blk_mq_hw_ctx *hctx,
 {
        struct nullb_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
 
+       might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
+
        if (irqmode == NULL_IRQ_TIMER) {
                hrtimer_init(&cmd->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
                cmd->timer.function = null_cmd_timer_expired;
@@ -724,6 +730,9 @@ static int null_add_dev(void)
                nullb->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
                nullb->tag_set.driver_data = nullb;
 
+               if (blocking)
+                       nullb->tag_set.flags |= BLK_MQ_F_BLOCKING;
+
                rv = blk_mq_alloc_tag_set(&nullb->tag_set);
                if (rv)
                        goto out_cleanup_queues;