[PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

[PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

[Arnd Bergmann]

gcc gets confused in pcpu_get_vm_areas() because there are too many
branches that affect whether 'lva' was initialized before it gets
used:

mm/vmalloc.c: In function 'pcpu_get_vm_areas':
mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    insert_vmap_area_augment(lva, &va->rb_node,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     &free_vmap_area_root, &free_vmap_area_list);
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/vmalloc.c:916:20: note: 'lva' was declared here
  struct vmap_area *lva;
                    ^~~

Add an intialization to NULL, and check whether this has changed
before the first use.

Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 mm/vmalloc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a9213fc3802d..42a6f795c3ee 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
 	unsigned long nva_start_addr, unsigned long size,
 	enum fit_type type)
 {
-	struct vmap_area *lva;
+	/*
+	 * GCC cannot always keep track of whether this variable
+	 * was initialized across many branches, therefore set
+	 * it NULL here to avoid a warning.
+	 */
+	struct vmap_area *lva = NULL;
 
 	if (type == FL_FIT_TYPE) {
 		/*
@@ -987,7 +992,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
 	if (type != FL_FIT_TYPE) {
 		augment_tree_propagate_from(va);
 
-		if (type == NE_FIT_TYPE)
+		if (lva)
 			insert_vmap_area_augment(lva, &va->rb_node,
 				&free_vmap_area_root, &free_vmap_area_list);
 	}
-- 
2.20.0

Re: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

[Joel Fernandes]

On Tue, Jun 18, 2019 at 5:27 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> gcc gets confused in pcpu_get_vm_areas() because there are too many
> branches that affect whether 'lva' was initialized before it gets
> used:
>
> mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>     insert_vmap_area_augment(lva, &va->rb_node,
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>      &free_vmap_area_root, &free_vmap_area_list);
>      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/vmalloc.c:916:20: note: 'lva' was declared here
>   struct vmap_area *lva;
>                     ^~~
>
> Add an intialization to NULL, and check whether this has changed
> before the first use.
>
> Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  mm/vmalloc.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a9213fc3802d..42a6f795c3ee 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
>         unsigned long nva_start_addr, unsigned long size,
>         enum fit_type type)
>  {
> -       struct vmap_area *lva;
> +       /*
> +        * GCC cannot always keep track of whether this variable
> +        * was initialized across many branches, therefore set
> +        * it NULL here to avoid a warning.
> +        */
> +       struct vmap_area *lva = NULL;

Fair enough, but is this 5-line comment really needed here?

- Joel

Re: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

[Uladzislau Rezki]

On Tue, Jun 18, 2019 at 09:40:28AM -0400, Joel Fernandes wrote:
> On Tue, Jun 18, 2019 at 5:27 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > gcc gets confused in pcpu_get_vm_areas() because there are too many
> > branches that affect whether 'lva' was initialized before it gets
> > used:
> >
> > mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >     insert_vmap_area_augment(lva, &va->rb_node,
> >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >      &free_vmap_area_root, &free_vmap_area_list);
> >      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > mm/vmalloc.c:916:20: note: 'lva' was declared here
> >   struct vmap_area *lva;
> >                     ^~~
> >
> > Add an intialization to NULL, and check whether this has changed
> > before the first use.
> >
> > Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  mm/vmalloc.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index a9213fc3802d..42a6f795c3ee 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
> >         unsigned long nva_start_addr, unsigned long size,
> >         enum fit_type type)
> >  {
> > -       struct vmap_area *lva;
> > +       /*
> > +        * GCC cannot always keep track of whether this variable
> > +        * was initialized across many branches, therefore set
> > +        * it NULL here to avoid a warning.
> > +        */
> > +       struct vmap_area *lva = NULL;
> 
> Fair enough, but is this 5-line comment really needed here?
> 
How it is rewritten now, probably not. I would just set it NULL and
leave the comment, but that is IMHO. Anyway

Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Thanks!

--
Vlad Rezki

Re: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

[Andrew Morton]

On Tue, 18 Jun 2019 16:06:22 +0200 Uladzislau Rezki <urezki@gmail.com> wrote:

> On Tue, Jun 18, 2019 at 09:40:28AM -0400, Joel Fernandes wrote:
> > On Tue, Jun 18, 2019 at 5:27 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > >
> > > gcc gets confused in pcpu_get_vm_areas() because there are too many
> > > branches that affect whether 'lva' was initialized before it gets
> > > used:
> > >
> > > mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> > > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > >     insert_vmap_area_augment(lva, &va->rb_node,
> > >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >      &free_vmap_area_root, &free_vmap_area_list);
> > >      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > mm/vmalloc.c:916:20: note: 'lva' was declared here
> > >   struct vmap_area *lva;
> > >                     ^~~
> > >
> > > Add an intialization to NULL, and check whether this has changed
> > > before the first use.
> > >
> > > Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > >  mm/vmalloc.c | 9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index a9213fc3802d..42a6f795c3ee 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
> > >         unsigned long nva_start_addr, unsigned long size,
> > >         enum fit_type type)
> > >  {
> > > -       struct vmap_area *lva;
> > > +       /*
> > > +        * GCC cannot always keep track of whether this variable
> > > +        * was initialized across many branches, therefore set
> > > +        * it NULL here to avoid a warning.
> > > +        */
> > > +       struct vmap_area *lva = NULL;
> > 
> > Fair enough, but is this 5-line comment really needed here?
> > 
> How it is rewritten now, probably not. I would just set it NULL and
> leave the comment, but that is IMHO. Anyway
> 

I agree - given that the patch does this:

@@ -972,7 +977,7 @@ adjust_va_to_fit_type(struct vmap_area *
 	if (type != FL_FIT_TYPE) {
 		augment_tree_propagate_from(va);
 
-		if (type == NE_FIT_TYPE)
+		if (lva)
 			insert_vmap_area_augment(lva, &va->rb_node,
 				&free_vmap_area_root, &free_vmap_area_list);
 	}

the comment simply isn't relevant any more.  Although I guess this
might be a bit helpful:

@@ -977,7 +972,7 @@ adjust_va_to_fit_type(struct vmap_area *
 	if (type != FL_FIT_TYPE) {
 		augment_tree_propagate_from(va);
 
-		if (lva)
+		if (lva)	/* type == NE_FIT_TYPE */
 			insert_vmap_area_augment(lva, &va->rb_node,
 				&free_vmap_area_root, &free_vmap_area_list);
 	}

Re: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

[Uladzislau Rezki]

On Tue, Jun 18, 2019 at 01:59:20PM -0700, Andrew Morton wrote:
> On Tue, 18 Jun 2019 16:06:22 +0200 Uladzislau Rezki <urezki@gmail.com> wrote:
> 
> > On Tue, Jun 18, 2019 at 09:40:28AM -0400, Joel Fernandes wrote:
> > > On Tue, Jun 18, 2019 at 5:27 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > > >
> > > > gcc gets confused in pcpu_get_vm_areas() because there are too many
> > > > branches that affect whether 'lva' was initialized before it gets
> > > > used:
> > > >
> > > > mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> > > > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > > >     insert_vmap_area_augment(lva, &va->rb_node,
> > > >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > >      &free_vmap_area_root, &free_vmap_area_list);
> > > >      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > mm/vmalloc.c:916:20: note: 'lva' was declared here
> > > >   struct vmap_area *lva;
> > > >                     ^~~
> > > >
> > > > Add an intialization to NULL, and check whether this has changed
> > > > before the first use.
> > > >
> > > > Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > > > ---
> > > >  mm/vmalloc.c | 9 +++++++--
> > > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index a9213fc3802d..42a6f795c3ee 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
> > > >         unsigned long nva_start_addr, unsigned long size,
> > > >         enum fit_type type)
> > > >  {
> > > > -       struct vmap_area *lva;
> > > > +       /*
> > > > +        * GCC cannot always keep track of whether this variable
> > > > +        * was initialized across many branches, therefore set
> > > > +        * it NULL here to avoid a warning.
> > > > +        */
> > > > +       struct vmap_area *lva = NULL;
> > > 
> > > Fair enough, but is this 5-line comment really needed here?
> > > 
> > How it is rewritten now, probably not. I would just set it NULL and
> > leave the comment, but that is IMHO. Anyway
> > 
> 
> I agree - given that the patch does this:
> 
> @@ -972,7 +977,7 @@ adjust_va_to_fit_type(struct vmap_area *
>  	if (type != FL_FIT_TYPE) {
>  		augment_tree_propagate_from(va);
>  
> -		if (type == NE_FIT_TYPE)
> +		if (lva)
>  			insert_vmap_area_augment(lva, &va->rb_node,
>  				&free_vmap_area_root, &free_vmap_area_list);
>  	}
> 
> the comment simply isn't relevant any more.  Although I guess this
> might be a bit helpful:
> 
> @@ -977,7 +972,7 @@ adjust_va_to_fit_type(struct vmap_area *
>  	if (type != FL_FIT_TYPE) {
>  		augment_tree_propagate_from(va);
>  
> -		if (lva)
> +		if (lva)	/* type == NE_FIT_TYPE */
>  			insert_vmap_area_augment(lva, &va->rb_node,
>  				&free_vmap_area_root, &free_vmap_area_list);
>  	}
> 
That comment makes it much clear, thanks!

--
Vlad Rezki