linux-kernel - Re: 4.5.0+ panic when setup loop device

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Date:	Thu, 17 Mar 2016 21:30:02 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jens Axboe <axboe@...nel.dk>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Xiong Zhou <jencce.kernel@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Andreas Herrmann <aherrmann@...e.com>
Subject: Re: 4.5.0+ panic when setup loop device

On Thu, 17 Mar 2016, Jens Axboe wrote:
> On 03/17/2016 01:20 PM, Thomas Gleixner wrote:
> > > This might be better, we need to start at -1 to not miss the first one...
> > > Still untested.
> > 
> > > +static inline struct blk_mq_ctx *next_ctx(struct request_queue *q, int
> > > *i)
> > > +{
> > > +	do {
> > > +		(*i)++;
> > > +		if (*i < q->nr_queues) {
> > > +			if (cpu_possible(*i))
> > > +				return per_cpu_ptr(q->queue_ctx, *i);
> > > +			continue;
> > > +		}
> > > +		break;
> > > +	} while (1);
> > > +
> > > +	return NULL;
> > > +}
> > > +
> > > +#define queue_for_each_ctx(q, ctx, i)
> > > \
> > > +	for ((i) = -1; (ctx = next_ctx((q), &(i))) != NULL;)
> > > +
> > 
> > What's wrong with
> > 
> >          for_each_possible_cpu(cpu) {
> >         		ctx = per_cpu_ptr(q->queue_ctx, cpu);
> > 
> > 		....
> > 	}
> > 
> > instead of hiding it behind an incomprehensible macro mess?
> 
> We might not have mapped all of them.

blk_mq_init_cpu_queues() tells a different story and q->queue_ctx is a per_cpu
allocation.

Thanks,

	tglx