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Subject: Re: [PATCH 2/5] nvme: don't hold nvmf_transports_rwsem for more than
 transport lookups
To:     Christoph Hellwig <hch@lst.de>,
        Johannes Thumshirn <jthumshirn@suse.de>
Cc:     Keith Busch <keith.busch@intel.com>,
        Linux NVMe Mailinglist <linux-nvme@lists.infradead.org>,
        Linux Kernel Mailinglist <linux-kernel@vger.kernel.org>,
        Hannes Reinecke <hare@suse.de>
References: <20180515074043.22843-1-jthumshirn@suse.de>
 <20180515074043.22843-3-jthumshirn@suse.de> <20180515074826.GA23659@lst.de>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <8577e467-ad74-d9bd-8f49-3ace18fc1126@grimberg.me>
Date:   Thu, 31 May 2018 12:24:51 +0300
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>> diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
>> index 7ae732a77fe8..febf82639b40 100644
>> --- a/drivers/nvme/host/fabrics.c
>> +++ b/drivers/nvme/host/fabrics.c
>> @@ -957,16 +957,17 @@ nvmf_create_ctrl(struct device *dev, const char *buf, size_t count)
>>   
>>   	down_read(&nvmf_transports_rwsem);
>>   	ops = nvmf_lookup_transport(opts);
>> +	up_read(&nvmf_transports_rwsem);
> 
> And what protects us from the transport getting unregister right here
> from anothet thread waiting to acquire nvmf_transports_rwsem?

I think having the module_get inside as well would protect against it.