linux-kernel - Re: [PATCH v2] nvme-multipath: Early exit if no path is available

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Message-ID: <20210128075837.u5u56t23fq5gu6ou@beryllium.lan>
Date:   Thu, 28 Jan 2021 08:58:37 +0100
From:   Daniel Wagner <dwagner@...e.de>
To:     Chao Leng <lengchao@...wei.com>
Cc:     linux-nvme@...ts.infradead.org, Sagi Grimberg <sagi@...mberg.me>,
        linux-kernel@...r.kernel.org, Jens Axboe <axboe@...com>,
        Hannes Reinecke <hare@...e.de>,
        Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available

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.