Linux Virtualization - Feb 2019 - [PATCH][next] vhost: only return early if ret indicates an error or no iovecs have been processed

From: Colin Ian King <colin.king at canonical.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 at canonical.com>
---
 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

On Tue, Feb 19, 2019 at 01:57:13PM +0000, Colin King
wrote:
> From: Colin Ian King <colin.king at canonical.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 at canonical.com>
Jason posted a similar patch recently.

Are you happy with that one?
> ---
>  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

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 at canonical.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 at canonical.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