linux-kernel - Re: [PATCH] RDMA/cm: fix cond_no

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Message-ID: <fdc5931f-5794-1770-0a5d-7470965cf390@nvidia.com>
Date:   Tue, 2 Aug 2022 10:15:24 +0800
From:   Mark Zhang <markzhang@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>, leon@...nel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Abaci Robot <abaci@...ux.alibaba.com>
Subject: Re: [PATCH] RDMA/cm: fix cond_no_effect.cocci warnings


> 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;
  }