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Subject: Re: [Xen-devel] [PATCH] xen-blkfront: fix kernel panic with
 negotiate_mq error path
To:     Juergen Gross <jgross@suse.com>, boris.ostrovsky@oracle.com,
        konrad.wilk@oracle.com, roger.pau@citrix.com
Cc:     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>
 <65b5d648-d9dc-9248-751c-b6e15109b52e@suse.com>
From:   Manjunath Patil <manjunath.b.patil@oracle.com>
Organization: Oracle Corporation
Message-ID: <bffbe7ff-afc9-c1b6-698f-fe3228a38760@oracle.com>
Date:   Tue, 30 Oct 2018 09:27:43 -0700
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Thank you Juergen for your comments.

I will soon send v2 patch.

-Thanks,
Manjunath
On 10/30/2018 12:04 AM, Juergen Gross wrote:
> On 29/10/2018 19:31, 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"
> Please us the correct format for specifying another commit.
>
>> Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
> Can you please add a "Fixes:" tag and "Cc: stable@vger.kernel.org" ?
>
>> ---
>>   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'd drop this change.
>
>>   
>>   	kfree(info->rinfo);
>>   	info->rinfo = NULL;
>> @@ -1919,6 +1921,7 @@ static int negotiate_mq(struct blkfront_info *info)
>>   			      GFP_KERNEL);
>>   	if (!info->rinfo) {
>>   		xenbus_dev_fatal(info->xbdev, -ENOMEM, "allocating ring_info structure");
>> +		info->nr_rings = 0;
>>   		return -ENOMEM;
>>   	}
>
> Juergen
>