[PATCH] RDMA/cm: fix cond_no_effect.cocci warnings

[PATCH] RDMA/cm: fix cond_no_effect.cocci warnings

[Jiapeng Chong]

This was found by coccicheck:

./drivers/infiniband/core/cm.c:685:7-9: WARNING: possible condition with no effect (if == else).

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
---
 drivers/infiniband/core/cm.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index 1c107d6d03b9..bb6a2b6b9657 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -676,14 +676,9 @@ static struct cm_id_private *cm_find_listen(struct ib_device *device,
 			refcount_inc(&cm_id_priv->refcount);
 			return cm_id_priv;
 		}
-		if (device < cm_id_priv->id.device)
+		if (device < cm_id_priv->id.device ||
+		    be64_lt(service_id, cm_id_priv->id.service_id))
 			node = node->rb_left;
-		else if (device > cm_id_priv->id.device)
-			node = node->rb_right;
-		else if (be64_lt(service_id, cm_id_priv->id.service_id))
-			node = node->rb_left;
-		else if (be64_gt(service_id, cm_id_priv->id.service_id))
-			node = node->rb_right;
 		else
 			node = node->rb_right;
 	}
-- 
2.20.1.7.g153144c

Re: [PATCH] RDMA/cm: fix cond_no_effect.cocci warnings

[Mark Zhang]

On 6/10/2022 5:45 PM, Jiapeng Chong wrote:
> This was found by coccicheck:
> 
> ./drivers/infiniband/core/cm.c:685:7-9: WARNING: possible condition with no effect (if == else).
> 
> Reported-by: Abaci Robot <abaci@linux.alibaba.com>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
> ---
>   drivers/infiniband/core/cm.c | 9 ++-------
>   1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> index 1c107d6d03b9..bb6a2b6b9657 100644
> --- a/drivers/infiniband/core/cm.c
> +++ b/drivers/infiniband/core/cm.c
> @@ -676,14 +676,9 @@ static struct cm_id_private *cm_find_listen(struct ib_device *device,
>   			refcount_inc(&cm_id_priv->refcount);
>   			return cm_id_priv;
>   		}
> -		if (device < cm_id_priv->id.device)
> +		if (device < cm_id_priv->id.device ||
> +		    be64_lt(service_id, cm_id_priv->id.service_id))
>   			node = node->rb_left;
> -		else if (device > cm_id_priv->id.device)
> -			node = node->rb_right;
> -		else if (be64_lt(service_id, cm_id_priv->id.service_id))
> -			node = node->rb_left;
> -		else if (be64_gt(service_id, cm_id_priv->id.service_id))
> -			node = node->rb_right;
>   		else
>   			node = node->rb_right;
>   	}

Not sure if the fix is correct, e.g. with this condition:
   device > cm_id_priv->id.device &&
   be64_lt(service_id, cm_id_priv->id.service_id)

The original code gets rb_right but this fix gets rb_left. Maybe the 
warning is complain about this:
	...
	else if (be64_gt(service_id, cm_id_priv->id.service_id))
		node = node->rb_right;
	else
		node = node->rb_right;

Besides cm_insert_listen() has same logic.

Re: [PATCH] RDMA/cm: fix cond_no_effect.cocci warnings

[Jason Gunthorpe]

On Tue, Jun 14, 2022 at 09:19:14AM +0800, Mark Zhang wrote:
> On 6/10/2022 5:45 PM, Jiapeng Chong wrote:
> > This was found by coccicheck:
> > 
> > ./drivers/infiniband/core/cm.c:685:7-9: WARNING: possible condition with no effect (if == else).
> > 
> > Reported-by: Abaci Robot <abaci@linux.alibaba.com>
> > Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
> > ---
> >   drivers/infiniband/core/cm.c | 9 ++-------
> >   1 file changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> > index 1c107d6d03b9..bb6a2b6b9657 100644
> > --- a/drivers/infiniband/core/cm.c
> > +++ b/drivers/infiniband/core/cm.c
> > @@ -676,14 +676,9 @@ static struct cm_id_private *cm_find_listen(struct ib_device *device,
> >   			refcount_inc(&cm_id_priv->refcount);
> >   			return cm_id_priv;
> >   		}
> > -		if (device < cm_id_priv->id.device)
> > +		if (device < cm_id_priv->id.device ||
> > +		    be64_lt(service_id, cm_id_priv->id.service_id))
> >   			node = node->rb_left;
> > -		else if (device > cm_id_priv->id.device)
> > -			node = node->rb_right;
> > -		else if (be64_lt(service_id, cm_id_priv->id.service_id))
> > -			node = node->rb_left;
> > -		else if (be64_gt(service_id, cm_id_priv->id.service_id))
> > -			node = node->rb_right;
> >   		else
> >   			node = node->rb_right;
> >   	}
> 
> Not sure if the fix is correct, e.g. with this condition:
>   device > cm_id_priv->id.device &&
>   be64_lt(service_id, cm_id_priv->id.service_id)
> 
> The original code gets rb_right but this fix gets rb_left. Maybe the warning
> is complain about this:
> 	...
> 	else if (be64_gt(service_id, cm_id_priv->id.service_id))
> 		node = node->rb_right;
> 	else
> 		node = node->rb_right;
> 
> Besides cm_insert_listen() has same logic.

Yes, this is a standard pattern for walking tree with priority, we
should not obfuscate it.

The final else means 'equal' and the first if should ideally be placed
there

However this function is complicated by the use of the service_mask
for equality checking, and it doesn't even work right if the
service_mask is not -1.

If someone wants to clean this then please go through and eliminate
service_mask completely. From what I can see its value is always -1.
Three patches:
 - Remove the service_mask parameter from ib_cm_listen(), all callers
   use 0
 - Remove the service_mask parameter from cm_init_listen(), all
   callers use 0. Inspect and remove cm_id_priv->id.service_mask,
   it is the constant value  ~cpu_to_be64(0) which is a NOP when &'d
 - Move the test at the top of cm_find_listen() into the final else

Jason

Re: [PATCH] RDMA/cm: fix cond_no_effect.cocci warnings

[Mark Zhang]

> Yes, this is a standard pattern for walking tree with priority, we
> should not obfuscate it.
> 
> The final else means 'equal' and the first if should ideally be placed
> there
> 
> However this function is complicated by the use of the service_mask
> for equality checking, and it doesn't even work right if the
> service_mask is not -1.
> 
> If someone wants to clean this then please go through and eliminate
> service_mask completely. From what I can see its value is always -1.
> Three patches:
>   - Remove the service_mask parameter from ib_cm_listen(), all callers
>     use 0
>   - Remove the service_mask parameter from cm_init_listen(), all
>     callers use 0. Inspect and remove cm_id_priv->id.service_mask,
>     it is the constant value  ~cpu_to_be64(0) which is a NOP when &'d
>   - Move the test at the top of cm_find_listen() into the final else
> 

I'll do it. For the 3rd one, do you mean a patch like (similar change in 
cm_insert_listen):

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index a2973436b16f..8749165bbe3d 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -626,9 +626,15 @@ static struct cm_id_private 
*cm_insert_listen(struct cm_id_private *cm_id_priv,
                 parent = *link;
                 cur_cm_id_priv = rb_entry(parent, struct cm_id_private,
                                           service_node);
-               if ((cur_cm_id_priv->id.service_mask & service_id) ==
-                   (service_mask & cur_cm_id_priv->id.service_id) &&
-                   (cm_id_priv->id.device == cur_cm_id_priv->id.device)) {
+               if (cm_id_priv->id.device < cur_cm_id_priv->id.device)
+                       link = &(*link)->rb_left;
+               else if (cm_id_priv->id.device > cur_cm_id_priv->id.device)
+                       link = &(*link)->rb_right;
+               else if (be64_lt(service_id, cur_cm_id_priv->id.service_id))
+                       link = &(*link)->rb_left;
+               else if (be64_gt(service_id, cur_cm_id_priv->id.service_id))
+                       link = &(*link)->rb_right;
+               else {
                         /*
                          * Sharing an ib_cm_id with different handlers 
is not
                          * supported
@@ -644,17 +650,6 @@ static struct cm_id_private 
*cm_insert_listen(struct cm_id_private *cm_id_priv,
                         spin_unlock_irqrestore(&cm.lock, flags);
                         return cur_cm_id_priv;
                 }
-
-               if (cm_id_priv->id.device < cur_cm_id_priv->id.device)
-                       link = &(*link)->rb_left;
-               else if (cm_id_priv->id.device > cur_cm_id_priv->id.device)
-                       link = &(*link)->rb_right;
-               else if (be64_lt(service_id, cur_cm_id_priv->id.service_id))
-                       link = &(*link)->rb_left;
-               else if (be64_gt(service_id, cur_cm_id_priv->id.service_id))
-                       link = &(*link)->rb_right;
-               else
-                       link = &(*link)->rb_right;
         }
         cm_id_priv->listen_sharecount++;
         rb_link_node(&cm_id_priv->service_node, parent, link);
@@ -671,12 +666,6 @@ static struct cm_id_private *cm_find_listen(struct 
ib_device *device,

         while (node) {
                 cm_id_priv = rb_entry(node, struct cm_id_private, 
service_node);
-               if ((cm_id_priv->id.service_mask & service_id) ==
-                    cm_id_priv->id.service_id &&
-                   (cm_id_priv->id.device == device)) {
-                       refcount_inc(&cm_id_priv->refcount);
-                       return cm_id_priv;
-               }
                 if (device < cm_id_priv->id.device)
                         node = node->rb_left;
                 else if (device > cm_id_priv->id.device)
@@ -685,8 +674,10 @@ static struct cm_id_private *cm_find_listen(struct 
ib_device *device,
                         node = node->rb_left;
                 else if (be64_gt(service_id, cm_id_priv->id.service_id))
                         node = node->rb_right;
-               else
-                       node = node->rb_right;
+               else {
+                       refcount_inc(&cm_id_priv->refcount);
+                       return cm_id_priv;
+               }
         }
         return NULL;
  }

Re: [PATCH] RDMA/cm: fix cond_no_effect.cocci warnings

[Jason Gunthorpe]

On Tue, Aug 02, 2022 at 10:15:24AM +0800, Mark Zhang wrote:
> 
> > Yes, this is a standard pattern for walking tree with priority, we
> > should not obfuscate it.
> > 
> > The final else means 'equal' and the first if should ideally be placed
> > there
> > 
> > However this function is complicated by the use of the service_mask
> > for equality checking, and it doesn't even work right if the
> > service_mask is not -1.
> > 
> > If someone wants to clean this then please go through and eliminate
> > service_mask completely. From what I can see its value is always -1.
> > Three patches:
> >   - Remove the service_mask parameter from ib_cm_listen(), all callers
> >     use 0
> >   - Remove the service_mask parameter from cm_init_listen(), all
> >     callers use 0. Inspect and remove cm_id_priv->id.service_mask,
> >     it is the constant value  ~cpu_to_be64(0) which is a NOP when &'d
> >   - Move the test at the top of cm_find_listen() into the final else
> > 
> 
> I'll do it. For the 3rd one, do you mean a patch like (similar change in
> cm_insert_listen):

Yes

Jason