[PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[Alakesh Haloi]

This patch fixes the following uninitialized variable warning

fs/proc/task_mmu.c: In function 'show_smap.isra.33':
fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
  bool last_vma;
       ^~~~~~~~

Cc: stable@vger.kernel.org # 4.14.x
Signed-off-by: Alakesh Haloi <alakesh.haloi@gmail.com>
---
 fs/proc/task_mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5e63c459dc61..50fc311ee458 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -758,7 +758,7 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
 	};
 	int ret = 0;
 	bool rollup_mode;
-	bool last_vma;
+	bool uninitialized_var(last_vma);
 
 	if (priv->rollup) {
 		rollup_mode = true;
-- 
2.17.2

Re: [PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[Greg Kroah-Hartman]

On Thu, Apr 18, 2019 at 01:20:12AM +0000, Alakesh Haloi wrote:
> This patch fixes the following uninitialized variable warning
> 
> fs/proc/task_mmu.c: In function 'show_smap.isra.33':
> fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
>   bool last_vma;
>        ^~~~~~~~
> 
> Cc: stable@vger.kernel.org # 4.14.x
> Signed-off-by: Alakesh Haloi <alakesh.haloi@gmail.com>
> ---
>  fs/proc/task_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

Re: [PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[Andrew Morton]

On Thu, 18 Apr 2019 01:20:12 +0000 Alakesh Haloi <alakesh.haloi@gmail.com> wrote:

> This patch fixes the following uninitialized variable warning
> 
> fs/proc/task_mmu.c: In function 'show_smap.isra.33':
> fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
>   bool last_vma;
>        ^~~~~~~~

I can't immediately find a kernel tree to which this is applicable. 
What kernel are you patching?

Re: [PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[Alakesh Haloi]

On Thu, Apr 18, 2019 at 03:34:59PM -0700, Andrew Morton wrote:
> On Thu, 18 Apr 2019 01:20:12 +0000 Alakesh Haloi <alakesh.haloi@gmail.com> wrote:
> 
> > This patch fixes the following uninitialized variable warning
> > 
> > fs/proc/task_mmu.c: In function 'show_smap.isra.33':
> > fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
> >   bool last_vma;
> >        ^~~~~~~~
> 
> I can't immediately find a kernel tree to which this is applicable. 
> What kernel are you patching?
> 
This is for 4.14 stable tree. Corresponding commit does not exist in
mainline as the code has changed.

Re: [PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[Greg Kroah-Hartman]

On Thu, Apr 25, 2019 at 12:34:19AM +0000, Alakesh Haloi wrote:
> On Thu, Apr 18, 2019 at 03:34:59PM -0700, Andrew Morton wrote:
> > On Thu, 18 Apr 2019 01:20:12 +0000 Alakesh Haloi <alakesh.haloi@gmail.com> wrote:
> > 
> > > This patch fixes the following uninitialized variable warning
> > > 
> > > fs/proc/task_mmu.c: In function 'show_smap.isra.33':
> > > fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
> > >   bool last_vma;
> > >        ^~~~~~~~
> > 
> > I can't immediately find a kernel tree to which this is applicable. 
> > What kernel are you patching?
> > 
> This is for 4.14 stable tree. Corresponding commit does not exist in
> mainline as the code has changed.

I suggest updating your compiler to a sane one, I do not see this
warning at all in the 4.14.y tree.

thanks,

greg k-h

Re: [PATCH] fs/proc/task_mmu.c: fix uninitalized variable warning

[Sasha Levin]

On Thu, Apr 25, 2019 at 08:47:41AM +0200, Greg Kroah-Hartman wrote:
>On Thu, Apr 25, 2019 at 12:34:19AM +0000, Alakesh Haloi wrote:
>> On Thu, Apr 18, 2019 at 03:34:59PM -0700, Andrew Morton wrote:
>> > On Thu, 18 Apr 2019 01:20:12 +0000 Alakesh Haloi <alakesh.haloi@gmail.com> wrote:
>> >
>> > > This patch fixes the following uninitialized variable warning
>> > >
>> > > fs/proc/task_mmu.c: In function 'show_smap.isra.33':
>> > > fs/proc/task_mmu.c:761:7: warning: 'last_vma' may be used uninitialized in this function [-Wmaybe-uninitialized]
>> > >   bool last_vma;
>> > >        ^~~~~~~~
>> >
>> > I can't immediately find a kernel tree to which this is applicable.
>> > What kernel are you patching?
>> >
>> This is for 4.14 stable tree. Corresponding commit does not exist in
>> mainline as the code has changed.
>
>I suggest updating your compiler to a sane one, I do not see this
>warning at all in the 4.14.y tree.

I've reproduced this warning using gcc 7.3, it looks like gcc 8.2 is
smart enough to understand that this is not actually an issue.

It was "fixed" upstream with 258f669e7e88 ("mm: /proc/pid/smaps_rollup:
convert to single value seq_file") which rewrote most of the code in
that area.

Given that this is a harmless warning that isn't seen with newer
compilers, I don't think it makes sense to do anything about it. I
figured I'd send this mail out just to have a record of this issue in
case it comes up again in the future.

--
Thanks,
Sasha