[PATCH] CodingStyle: add some more error handling guidelines

Michael S. Tsirkin
2016-08-22T13:57:56Z

commit commit ea04036032edda6f771c1381d03832d2ed0f6c31 ("CodingStyle:
add some more error handling guidelines") suggests never naming goto
labels after the goto location - that is the error that is handled.

But it's actually pretty common and IMHO it's a reasonable style
provided each error gets its own label, and each label comes after the
matching cleanup:

foo = kmalloc(SIZE, GFP_KERNEL);
if (!foo)
goto err_foo;

foo->bar = kmalloc(SIZE, GFP_KERNEL);
if (!foo->bar)
goto err_bar;
...

kfree(foo->bar);
err_bar:

kfree(foo);
err_foo:

return ret;

Provides some symmetry and makes it easy to add more cases as code
calling goto does not need to worry about how is the error handled.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Jonathan Corbet <corbet@lwn.net>
---
tools/virtio/ringtest/main.h | 4 +++-
Documentation/CodingStyle | 44 ++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/tools/virtio/ringtest/main.h b/tools/virtio/ringtest/main.h
index 16917ac..e4d76c3 100644
--- a/tools/virtio/ringtest/main.h
+++ b/tools/virtio/ringtest/main.h
@@ -80,7 +80,9 @@ extern unsigned ring_size;

/* Is there a portable way to do this? */
#if defined(__x86_64__) || defined(__i386__)
-#define cpu_relax() asm ("rep; nop" ::: "memory")
+#define cpu_relax() do { \
+ asm ("rep; nop" ::: "memory"); \
+} while (0)
#else
#define cpu_relax() assert(0)
#endif
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index a096836..af2b5e9 100644
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -397,8 +397,7 @@ cleanup needed then just return directly.

Choose label names which say what the goto does or why the goto exists. An
example of a good name could be "out_buffer:" if the goto frees "buffer". Avoid
-using GW-BASIC names like "err1:" and "err2:". Also don't name them after the
-goto location like "err_kmalloc_failed:"
+using GW-BASIC names like "err1:" and "err2:".

The rationale for using gotos is:

@@ -440,6 +439,47 @@ A common type of bug to be aware of is "one err bugs" which look like this:
The bug in this code is that on some exit paths "foo" is NULL. Normally the
fix for this is to split it up into two error labels "err_bar:" and "err_foo:".

+Note that labels normally come before the appropriate cleanups:
+
+ foo = kmalloc(SIZE, GFP_KERNEL);
+ if (!foo)
+ goto out;
+
+ foo->bar = kmalloc(SIZE, GFP_KERNEL);
+ if (!foo->bar)
+ goto out_foo;
+ ...
+ if (err)
+ goto out_bar;
+
+ out_bar:
+ kfree(foo->bar);
+
+ out_foo:
+ kfree(foo);
+
+ out:
+ return ret;
+
+If labels are named after the goto location (or error that was detected), they
+come after the matching cleanup code:
+
+ foo = kmalloc(SIZE, GFP_KERNEL);
+ if (!foo)
+ goto err_foo;
+
+ foo->bar = kmalloc(SIZE, GFP_KERNEL);
+ if (!foo->bar)
+ goto err_bar;
+ ...
+
+ kfree(foo->bar);
+ err_bar:
+
+ kfree(foo);
+ err_foo:
+
+ return ret;

Chapter 8: Commenting

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MST