linux-kernel - RE: Drivers: hv: vmbus: One function call less in create_gpadl

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Date: Wed, 10 Jan 2024 16:15:42 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Markus Elfring <Markus.Elfring@....de>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "kernel-janitors@...r.kernel.org"
	<kernel-janitors@...r.kernel.org>, Dexuan Cui <decui@...rosoft.com>, Haiyang
 Zhang <haiyangz@...rosoft.com>, "K. Y. Srinivasan" <kys@...rosoft.com>, Wei
 Liu <wei.liu@...nel.org>, "cocci@...ia.fr" <cocci@...ia.fr>
CC: LKML <linux-kernel@...r.kernel.org>
Subject: RE: Drivers: hv: vmbus: One function call less in
 create_gpadl_header() after error detection

From: Markus Elfring <Markus.Elfring@....de> Sent: Wednesday, January 10, 2024 2:58 AM
> 
> >> The kfree() function was called in two cases by
> >> the create_gpadl_header() function during error handling
> >> even if the passed variable contained a null pointer.
> >> This issue was detected by using the Coccinelle software.
> >>
> >> Thus use another label.
> >
> > Interestingly, there's a third case in this function where
> > "goto nomem" is done, and in this case, msgbody is NULL.
> > Does Coccinelle not complain about that case as well?
> >
> > As I'm sure you know, the code is correct as is, because kfree()
> > checks for a NULL argument.  So this is really an exercise in
> > making Coccinelle happy.  To me, the additional label is
> > incremental complexity for someone to deal with when
> > reading the code at some time in the future.  So I'd vote for
> > leaving the code as is.  But it's not a big deal either way.  I
> > can see you've been cleaning up a lot of Coccinelle-reported
> > issues across the kernel, most of which result in code
> > simplifications.  If leaving this unchanged causes you problems,
> > then I won't object (though perhaps that 3rd "goto nomem"
> > should be dealt with as well for consistency).
> 
> How do you think about the clarification approach
> “Reconsidering kfree() calls for null pointers (with SmPL)”?
> https://lore.kernel.org/cocci/6cbcf640-55e5-2f11-4a09-716fe681c0d2@web.de/
> https://sympa.inria.fr/sympa/arc/cocci/2023-03/msg00096.html
> 

It occurred to me overnight that the existing error handling
in create_gpadl_header() is unnecessarily complicated.  Here's
an approach that I think would fix what you have flagged, and
would reduce complexity instead of increasing it.  Thoughts?

Michael

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 56f7e06c673e..44b1d5c8dfed 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -336,7 +336,7 @@ static int create_gpadl_header(enum hv_gpadl_type type, void *kbuffer,
 			  sizeof(struct gpa_range) + pfncount * sizeof(u64);
 		msgheader =  kzalloc(msgsize, GFP_KERNEL);
 		if (!msgheader)
-			goto nomem;
+			return -ENOMEM;
 
 		INIT_LIST_HEAD(&msgheader->submsglist);
 		msgheader->msgsize = msgsize;
@@ -386,8 +386,8 @@ static int create_gpadl_header(enum hv_gpadl_type type, void *kbuffer,
 					list_del(&pos->msglistentry);
 					kfree(pos);
 				}
-
-				goto nomem;
+				kfree(msgheader);
+				return -ENOMEM;
 			}
 
 			msgbody->msgsize = msgsize;
@@ -416,8 +416,8 @@ static int create_gpadl_header(enum hv_gpadl_type type, void *kbuffer,
 			  sizeof(struct vmbus_channel_gpadl_header) +
 			  sizeof(struct gpa_range) + pagecount * sizeof(u64);
 		msgheader = kzalloc(msgsize, GFP_KERNEL);
-		if (msgheader == NULL)
-			goto nomem;
+		if (!msgheader)
+			return -ENOMEM;
 
 		INIT_LIST_HEAD(&msgheader->submsglist);
 		msgheader->msgsize = msgsize;
@@ -437,10 +437,6 @@ static int create_gpadl_header(enum hv_gpadl_type type, void *kbuffer,
 	}
 
 	return 0;
-nomem:
-	kfree(msgheader);
-	kfree(msgbody);
-	return -ENOMEM;
 }
 
 /*