On Tuesday 09 October 2012, Arnd Bergmann wrote:

On Monday 08 October 2012, Jan Kara wrote:

quoted

On Fri 05-10-12 16:55:19, Arnd Bergmann wrote:

quoted

The follow_link() function always initializes its *p argument,
or returns an error, but not all versions of gcc figure this
out, so we have to work around this using the uninitialized_var()
macro.

  Well, I'm somewhat sceptical to this approach. I agree that bogus
warnings are not nice but later when the code is changed and possibly real
use without initialization is added, we won't notice it. Without changing
anything, we'd at least have a chance of catching it with gcc versions
which were clever enough to not warn with the original code. Or
alternatively if we unconditionally initialized the variable that would get
rid of the warning and made the code more future-proof (that's what I
usually end up doing)... I don't really care that much about the chosen
solution, Al is the one to decide. But I wanted to point out there are
downsides to your solution.

I'll drop the patch for now and won't send it from my tree then. I agree
that uninitialized_var() is not ideal, but none of the alternatives seemed
better.

With my latest compiler, I don't actually see the warnings any more, so
maybe someone fixed gcc instead, or this went away after another change.
I'll let you know if it comes back so we can discuss about a better fix then.

Update: I could actually reproduce the problem now, but it only happens when
building with 'gcc -s' (i.e. CONFIG_CC_OPTIMIZE_FOR_SIZE). It does happen
with both gcc-4.6 and with gcc-4.8, and on both x86-64 and ARM. An alternative
patch that would also make it go away is the variant below, but I think that's
even worse than the first version I suggested because it makes the binary
output slightly worse by adding an unnecessary initialization when building with
'make -s'.

	Arnd

diff --git a/fs/namei.c b/fs/namei.c
index aa30d19..c3612a5 100644
--- a/fs/namei.c
+++ b/fs/namei.c

@@ -810,6 +810,7 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 	return error;
 
 out_put_nd_path:
+	*p = NULL;
 	path_put(&nd->path);
 	path_put(link);
 	return error;