linux-kernel - Re: [PATCH][next] vhost: only return early if ret indicates an error or no iovecs have been processed

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Message-ID: <4145121c-83b8-e4a4-6c95-ee0151ac70c0@canonical.com>
Date:   Tue, 19 Feb 2019 16:40:45 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] vhost: only return early if ret indicates an error
 or no iovecs have been processed

On 19/02/2019 16:35, Michael S. Tsirkin wrote:
> On Tue, Feb 19, 2019 at 01:57:13PM +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> Currently the loop that calls log_write_hva on each iovec is never
>> executed because of an incorrect error check on the return from the
>> call to translate_desc.  The check should be checking for a -ve error
>> return and because it makes no sense to iterate over zero items, the
>> checks should also check for zero too.
>>
>> Detected by CoverityScan, CID#1476969 ("Logically dead code")
>>
>> Fixes: cc5e71075947 ("vhost: log dirty page correctly")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> 
> Jason posted a similar patch recently.
> 
> Are you happy with that one?

Sure, ignore mine, I was late to the party.

> 
>> ---
>>  drivers/vhost/vhost.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 24a129fcdd61..a9a1709a859a 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -1788,7 +1788,7 @@ static int log_used(struct vhost_virtqueue *vq, u64 used_offset, u64 len)
>>  
>>  	ret = translate_desc(vq, (uintptr_t)vq->used + used_offset,
>>  			     len, iov, 64, VHOST_ACCESS_WO);
>> -	if (ret)
>> +	if (ret <= 0)
>>  		return ret;
>>  
>>  	for (i = 0; i < ret; i++) {
>> -- 
>> 2.20.1