null_blk: prevent timer handler running on a different CPU where started

When irqmode=2 (IRQ completion handler is timer), timer handler should
be called on the same CPU where the timer has been started.

Since completion_queues are per-cpu and the completion handler only
touches completion_queue for local CPU, we need to prevent the handler
from running on a different CPU where the timer has been started.
Otherwise, the IO cannot be completed until another completion handler
is executed on that CPU.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 65cd61a4145ed2049944621c50b374cf742041ca..6f0a58e7613db5e499e70c7b5f7ffec804d429bf 100644 (file)
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -257,7 +257,7 @@ static void null_cmd_end_timer(struct nullb_cmd *cmd)
        if (llist_add(&cmd->ll_list, &cq->list)) {
                ktime_t kt = ktime_set(0, completion_nsec);
 
-               hrtimer_start(&cq->timer, kt, HRTIMER_MODE_REL);
+               hrtimer_start(&cq->timer, kt, HRTIMER_MODE_REL_PINNED);
        }
 
        put_cpu();