Re: Summary so far - ubd breakage in 4.20-rc1

From: Richard Weinberger <richard@nod.at>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-um@lists.infradead.org,
	Anton Ivanov <anton.ivanov@kot-begemot.co.uk>,
	hch@lst.de
Subject: Re: Summary so far - ubd breakage in 4.20-rc1
Date: Wed, 07 Nov 2018 22:46:13 +0100	[thread overview]
Message-ID: <4373302.HifUKF8Eoy@blindfold> (raw)
In-Reply-To: <fe020526-ac24-0279-ca27-7ccabba7a6cc@kernel.dk>

Am Mittwoch, 7. November 2018, 22:16:20 CET schrieb Jens Axboe:
> >> Does the below help things?
> >>
> > 
> > It does!
> > Anton, please give it also a try.
> 
> OK good, it's definitely a bug, and given the symptoms, sounds like
> THE bug in this case.

Shall I send your fix as patch or do you want to?

> >> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> >> index 74c002ddc0ce..019bc4828e30 100644
> >> --- a/arch/um/drivers/ubd_kern.c
> >> +++ b/arch/um/drivers/ubd_kern.c
> >> @@ -1341,11 +1341,14 @@ static int ubd_queue_one_vec(struct blk_mq_hw_ctx *hctx, struct request *req,
> >>  static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
> >>  				 const struct blk_mq_queue_data *bd)
> >>  {
> >> +	struct ubd *ubd_dev = hctx->queue->queuedata;
> >>  	struct request *req = bd->rq;
> >>  	int ret = 0;
> >>  
> >>  	blk_mq_start_request(req);
> >>  
> >> +	spin_lock_irq(&ubd_dev->lock);
> >> +
> > 
> > BTW: Why not irq_save/restore?
> 
> You only need the save/restore versions if you're called with
> interrupts already disabled (or may be), that's not the case
> here. Hence we can use the faster versions.

Got it!

Thanks,
//richard

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