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Subject: Re: [PATCH 11/14] irq: add support for allocating (and affinitizing)
 sets of IRQs
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Keith Busch <keith.busch@intel.com>, linux-block@vger.kernel.org,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <a692fbb3-59ca-0ddb-7abd-67ffc7bfcc1f@kernel.dk>
Date:   Tue, 30 Oct 2018 11:34:32 -0600
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On 10/30/18 11:25 AM, Thomas Gleixner wrote:
> Jens,
> 
> On Tue, 30 Oct 2018, Jens Axboe wrote:
>> On 10/30/18 10:02 AM, Keith Busch wrote:
>>> pci_alloc_irq_vectors_affinity() starts at the provided max_vecs. If
>>> that doesn't work, it will iterate down to min_vecs without returning to
>>> the caller. The caller doesn't have a chance to adjust its sets between
>>> iterations when you provide a range.
>>>
>>> The 'masks' overrun problem happens if the caller provides min_vecs
>>> as a smaller value than the sum of the set (plus any reserved).
>>>
>>> If it's up to the caller to ensure that doesn't happen, then min and
>>> max must both be the same value, and that value must also be the same as
>>> the set sum + reserved vectors. The range just becomes redundant since
>>> it is already bounded by the set.
>>>
>>> Using the nvme example, it would need something like this to prevent the
>>> 'masks' overrun:
>>
>> OK, now I hear what you are saying. And you are right, the callers needs
>> to provide minvec == maxvec for sets, and then have a loop around that
>> to adjust as needed.
> 
> But then we should enforce it in the core code, right?

Yes, I was going to ask you if you want a followup patch for that, or
an updated version of the original?

-- 
Jens Axboe