Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [Xen-devel] [PATCH] xen-blkfront: fix kernel panic with
 negotiate_mq error path
To:     =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Cc:     boris.ostrovsky@oracle.com, jgross@suse.com,
        konrad.wilk@oracle.com, axboe@kernel.dk,
        xen-devel@lists.xenproject.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1540837916-14356-1-git-send-email-manjunath.b.patil@oracle.com>
 <20181030103956.hew7gifjvpjviw7u@mac.citrite.net>
From:   Manjunath Patil <manjunath.b.patil@oracle.com>
Organization: Oracle Corporation
Message-ID: <f8b9a166-e844-018d-2186-b49f54fc6fbb@oracle.com>
Date:   Tue, 30 Oct 2018 09:29:02 -0700
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <20181030103956.hew7gifjvpjviw7u@mac.citrite.net>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 10/30/2018 3:39 AM, Roger Pau Monné wrote:

> On Mon, Oct 29, 2018 at 11:31:56AM -0700, Manjunath Patil wrote:
>> info->nr_rings isn't adjusted in case of ENOMEM error from
>> negotiate_mq(). This leads to kernel panic in error path.
>>
>> Typical call stack involving panic -
>>   #8 page_fault at ffffffff8175936f
>>      [exception RIP: blkif_free_ring+33]
>>      RIP: ffffffffa0149491  RSP: ffff8804f7673c08  RFLAGS: 00010292
>>   ...
>>   #9 blkif_free at ffffffffa0149aaa [xen_blkfront]
>>   #10 talk_to_blkback at ffffffffa014c8cd [xen_blkfront]
>>   #11 blkback_changed at ffffffffa014ea8b [xen_blkfront]
>>   #12 xenbus_otherend_changed at ffffffff81424670
>>   #13 backend_changed at ffffffff81426dc3
>>   #14 xenwatch_thread at ffffffff81422f29
>>   #15 kthread at ffffffff810abe6a
>>   #16 ret_from_fork at ffffffff81754078
>>
>> Though either of my changes avoid the panic, I included both the
>> changes. This issue got introduced with "7ed8ce1 xen-blkfront: move
>> negotiate_mq to cover all cases of new VBDs"
>>
>> Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
>> ---
>>   drivers/block/xen-blkfront.c |    7 +++++--
>>   1 files changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 429d201..dc8fe25 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -1350,8 +1350,10 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>>   	if (info->rq)
>>   		blk_mq_stop_hw_queues(info->rq);
>>   
>> -	for (i = 0; i < info->nr_rings; i++)
>> -		blkif_free_ring(&info->rinfo[i]);
>> +	if (info->rinfo) {
>> +		for (i = 0; i < info->nr_rings; i++)
>> +			blkif_free_ring(&info->rinfo[i]);
>> +	}
> I don't see the point in the if case here, you already fixed it by
> setting the nr_rings value which I think it's the correct way of
> fixing it.
>
> Thanks, Roger.
Thank you Roger for your comments.
I will exclude this change and send for review again.

-Thanks,
Manjunath