From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S936813AbcCQUl3 (ORCPT <rfc822;w@1wt.eu>);
	Thu, 17 Mar 2016 16:41:29 -0400
Received: from mail-pf0-f182.google.com ([209.85.192.182]:36792 "EHLO
	mail-pf0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932357AbcCQUlZ (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 17 Mar 2016 16:41:25 -0400
Subject: Re: 4.5.0+ panic when setup loop device
To: Thomas Gleixner <tglx@linutronix.de>
References: <CADJHv_ty-8OsX3YKKYg4vtzcL-Hmag3rtjObbcgFLE-KLt1M7g@mail.gmail.com>
 <alpine.DEB.2.11.1603161624280.3978@nanos>
 <CADJHv_s1cM=NxkCSHEm_1MctDYJUkDtutLB=aFtx9rB4a3FZdw@mail.gmail.com>
 <20160317095220.GO6344@twins.programming.kicks-ass.net>
 <alpine.DEB.2.11.1603171119060.3978@nanos>
 <20160317102633.GR6344@twins.programming.kicks-ass.net>
 <alpine.DEB.2.11.1603171223480.3978@nanos>
 <20160317115120.GT6344@twins.programming.kicks-ass.net>
 <alpine.DEB.2.11.1603171258260.3978@nanos> <56EADE5F.7000601@kernel.dk>
 <56EAF6CC.7070108@kernel.dk> <alpine.DEB.2.11.1603172113470.3978@nanos>
 <56EB124C.2040808@kernel.dk> <alpine.DEB.2.11.1603172128280.3978@nanos>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Xiong Zhou <jencce.kernel@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Andreas Herrmann <aherrmann@suse.com>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <56EB1672.7000002@kernel.dk>
Date: Thu, 17 Mar 2016 13:41:22 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.6.0
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.11.1603172128280.3978@nanos>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 03/17/2016 01:30 PM, Thomas Gleixner wrote:
> 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.

Yeah my bad, I mistook the possible for online. So we can do the easier fix.

-- 
Jens Axboe