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Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available
To:     Daniel Wagner <dwagner@suse.de>
CC:     <linux-nvme@lists.infradead.org>, Sagi Grimberg <sagi@grimberg.me>,
        <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@fb.com>,
        Hannes Reinecke <hare@suse.de>,
        Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de>
References: <20210127103033.15318-1-dwagner@suse.de>
 <db9baae0-547c-7ff4-8b2c-0b95f14be67c@huawei.com>
 <20210128075837.u5u56t23fq5gu6ou@beryllium.lan>
From:   Chao Leng <lengchao@huawei.com>
Message-ID: <69575290-200e-b4a1-4269-c71e4c2cc37b@huawei.com>
Date:   Thu, 28 Jan 2021 17:18:56 +0800
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On 2021/1/28 15:58, Daniel Wagner wrote:
> On Thu, Jan 28, 2021 at 09:31:30AM +0800, Chao Leng wrote:
>>> --- a/drivers/nvme/host/multipath.c
>>> +++ b/drivers/nvme/host/multipath.c
>>> @@ -221,7 +221,7 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head,
>>>    	}
>>>    	for (ns = nvme_next_ns(head, old);
>>> -	     ns != old;
>>> +	     ns && ns != old;
>> nvme_round_robin_path just be called when !"old".
>> nvme_next_ns should not return NULL when !"old".
>> It seems unnecessary to add checking "ns".
> 
> The problem is when we enter nvme_round_robin_path() and there is no
> path available. In this case the initialization ns = nvme_next_ns(head,
> old) could return a NULL pointer."old" should not be NULL, so there is at least one path that is "old".
It is impossible to return NULL for nvme_next_ns(head, old).
> .
>