[PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Uladzislau Rezki (Sony)]

Before triggering a BUG() it would be useful to understand
how two areas overlap between each other. Print information
about start/end addresses of both VAs and their addresses.

For example if both are identical it could mean double free.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 mm/vmalloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5a2b55c8dd9a..1679b01febcd 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
 		else if (va->va_end > tmp_va->va_start &&
 				va->va_start >= tmp_va->va_end)
 			link = &(*link)->rb_right;
-		else
+		else {
+			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
+				va, va->va_start, va->va_end, tmp_va,
+				tmp_va->va_start, tmp_va->va_end);
+
 			BUG();
+		}
 	} while (*link);
 
 	*parent = &tmp_va->rb_node;
@@ -1993,6 +1998,9 @@ static void vmap_init_free_space(void)
 			insert_vmap_area_augment(free, NULL,
 				&free_vmap_area_root,
 					&free_vmap_area_list);
+			insert_vmap_area_augment(free, NULL,
+				&free_vmap_area_root,
+					&free_vmap_area_list);
 		}
 	}
 }
-- 
2.20.1

Re: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Uladzislau Rezki]

> Before triggering a BUG() it would be useful to understand
> how two areas overlap between each other. Print information
> about start/end addresses of both VAs and their addresses.
> 
> For example if both are identical it could mean double free.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> ---
>  mm/vmalloc.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 5a2b55c8dd9a..1679b01febcd 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
>  		else if (va->va_end > tmp_va->va_start &&
>  				va->va_start >= tmp_va->va_end)
>  			link = &(*link)->rb_right;
> -		else
> +		else {
> +			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
> +				va, va->va_start, va->va_end, tmp_va,
> +				tmp_va->va_start, tmp_va->va_end);
> +
>  			BUG();
> +		}
>  	} while (*link);
>  
>  	*parent = &tmp_va->rb_node;
> @@ -1993,6 +1998,9 @@ static void vmap_init_free_space(void)
>  			insert_vmap_area_augment(free, NULL,
>  				&free_vmap_area_root,
>  					&free_vmap_area_list);
> +			insert_vmap_area_augment(free, NULL,
> +				&free_vmap_area_root,
> +					&free_vmap_area_list);
>  		}
>  	}
>  }
> 
Please ignore this patch, i will upload v2.

Sorry for inconvenience.

--
Vlad Rezki

Re: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Matthew Wilcox]

On Fri, Jul 10, 2020 at 09:40:42PM +0200, Uladzislau Rezki (Sony) wrote:
> Before triggering a BUG() it would be useful to understand
> how two areas overlap between each other. Print information
> about start/end addresses of both VAs and their addresses.
> 
> For example if both are identical it could mean double free.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> ---
>  mm/vmalloc.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 5a2b55c8dd9a..1679b01febcd 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
>  		else if (va->va_end > tmp_va->va_start &&
>  				va->va_start >= tmp_va->va_end)
>  			link = &(*link)->rb_right;
> -		else
> +		else {
> +			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
> +				va, va->va_start, va->va_end, tmp_va,
> +				tmp_va->va_start, tmp_va->va_end);

It might be helpful to have a "vmalloc:" prefix to that string to indicate
where to start searching.  And I don't think we're supposed to use %px
without a really good justification these days.

Can we do without the BUG()?  Maybe just break out and decline to insert
the conflicting range?

>  			BUG();
> +		}
>  	} while (*link);
>  
>  	*parent = &tmp_va->rb_node;
> @@ -1993,6 +1998,9 @@ static void vmap_init_free_space(void)
>  			insert_vmap_area_augment(free, NULL,
>  				&free_vmap_area_root,
>  					&free_vmap_area_list);
> +			insert_vmap_area_augment(free, NULL,
> +				&free_vmap_area_root,
> +					&free_vmap_area_list);

This is surely testing code that you forgot to delete?

Re: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Uladzislau Rezki]

On Fri, Jul 10, 2020 at 08:44:06PM +0100, Matthew Wilcox wrote:
> On Fri, Jul 10, 2020 at 09:40:42PM +0200, Uladzislau Rezki (Sony) wrote:
> > Before triggering a BUG() it would be useful to understand
> > how two areas overlap between each other. Print information
> > about start/end addresses of both VAs and their addresses.
> > 
> > For example if both are identical it could mean double free.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > ---
> >  mm/vmalloc.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 5a2b55c8dd9a..1679b01febcd 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
> >  		else if (va->va_end > tmp_va->va_start &&
> >  				va->va_start >= tmp_va->va_end)
> >  			link = &(*link)->rb_right;
> > -		else
> > +		else {
> > +			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
> > +				va, va->va_start, va->va_end, tmp_va,
> > +				tmp_va->va_start, tmp_va->va_end);
> 
> It might be helpful to have a "vmalloc:" prefix to that string to indicate
> where to start searching.  And I don't think we're supposed to use %px
> without a really good justification these days.
> 
> Can we do without the BUG()?  Maybe just break out and decline to insert
> the conflicting range?
> 
> >  			BUG();
> > +		}
> >  	} while (*link);
> >  
> >  	*parent = &tmp_va->rb_node;
> > @@ -1993,6 +1998,9 @@ static void vmap_init_free_space(void)
> >  			insert_vmap_area_augment(free, NULL,
> >  				&free_vmap_area_root,
> >  					&free_vmap_area_list);
> > +			insert_vmap_area_augment(free, NULL,
> > +				&free_vmap_area_root,
> > +					&free_vmap_area_list);
> 
> This is surely testing code that you forgot to delete?
Matthew, you are super fast!!! :)

--
Vlad Rezki

Re: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Uladzislau Rezki]

On Fri, Jul 10, 2020 at 08:44:06PM +0100, Matthew Wilcox wrote:
> On Fri, Jul 10, 2020 at 09:40:42PM +0200, Uladzislau Rezki (Sony) wrote:
> > Before triggering a BUG() it would be useful to understand
> > how two areas overlap between each other. Print information
> > about start/end addresses of both VAs and their addresses.
> > 
> > For example if both are identical it could mean double free.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > ---
> >  mm/vmalloc.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 5a2b55c8dd9a..1679b01febcd 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
> >  		else if (va->va_end > tmp_va->va_start &&
> >  				va->va_start >= tmp_va->va_end)
> >  			link = &(*link)->rb_right;
> > -		else
> > +		else {
> > +			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
> > +				va, va->va_start, va->va_end, tmp_va,
> > +				tmp_va->va_start, tmp_va->va_end);
> 
> It might be helpful to have a "vmalloc:" prefix to that string to indicate
> where to start searching.  And I don't think we're supposed to use %px
> without a really good justification these days.
>
That makes sense, i will add such prefix for sure. As for %px i can just
use a casting to (unsigned long) and 0x%lx prefix.

> 
> Can we do without the BUG()?  Maybe just break out and decline to insert
> the conflicting range?
> 
When i developed that logic, i was thinking about that but for some
reason i went with BUG_ON(), do not remember why. But i agree we shold
avoid of it. Let me think about it one more time.

> >  			BUG();
> > +		}
> >  	} while (*link);
> >  
> >  	*parent = &tmp_va->rb_node;
> > @@ -1993,6 +1998,9 @@ static void vmap_init_free_space(void)
> >  			insert_vmap_area_augment(free, NULL,
> >  				&free_vmap_area_root,
> >  					&free_vmap_area_list);
> > +			insert_vmap_area_augment(free, NULL,
> > +				&free_vmap_area_root,
> > +					&free_vmap_area_list);
> 
> This is surely testing code that you forgot to delete?
>
Yes, i forgot to remove it.

Thanks for your comments!

--
Vlad Rezki

Re: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Matthew Wilcox]

On Fri, Jul 10, 2020 at 10:00:30PM +0200, Uladzislau Rezki wrote:
> On Fri, Jul 10, 2020 at 08:44:06PM +0100, Matthew Wilcox wrote:
> > On Fri, Jul 10, 2020 at 09:40:42PM +0200, Uladzislau Rezki (Sony) wrote:
> > > Before triggering a BUG() it would be useful to understand
> > > how two areas overlap between each other. Print information
> > > about start/end addresses of both VAs and their addresses.
> > > 
> > > For example if both are identical it could mean double free.
> > > 
> > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > ---
> > >  mm/vmalloc.c | 10 +++++++++-
> > >  1 file changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 5a2b55c8dd9a..1679b01febcd 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
> > >  		else if (va->va_end > tmp_va->va_start &&
> > >  				va->va_start >= tmp_va->va_end)
> > >  			link = &(*link)->rb_right;
> > > -		else
> > > +		else {
> > > +			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
> > > +				va, va->va_start, va->va_end, tmp_va,
> > > +				tmp_va->va_start, tmp_va->va_end);
> > 
> > It might be helpful to have a "vmalloc:" prefix to that string to indicate
> > where to start searching.  And I don't think we're supposed to use %px
> > without a really good justification these days.
> >
> That makes sense, i will add such prefix for sure. As for %px i can just
> use a casting to (unsigned long) and 0x%lx prefix.

That's not the point.  Linus wants us to not display actual pointers to
the user.

Re: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

[Uladzislau Rezki]

On Fri, Jul 10, 2020 at 09:01:38PM +0100, Matthew Wilcox wrote:
> On Fri, Jul 10, 2020 at 10:00:30PM +0200, Uladzislau Rezki wrote:
> > On Fri, Jul 10, 2020 at 08:44:06PM +0100, Matthew Wilcox wrote:
> > > On Fri, Jul 10, 2020 at 09:40:42PM +0200, Uladzislau Rezki (Sony) wrote:
> > > > Before triggering a BUG() it would be useful to understand
> > > > how two areas overlap between each other. Print information
> > > > about start/end addresses of both VAs and their addresses.
> > > > 
> > > > For example if both are identical it could mean double free.
> > > > 
> > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > > ---
> > > >  mm/vmalloc.c | 10 +++++++++-
> > > >  1 file changed, 9 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index 5a2b55c8dd9a..1679b01febcd 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
> > > >  		else if (va->va_end > tmp_va->va_start &&
> > > >  				va->va_start >= tmp_va->va_end)
> > > >  			link = &(*link)->rb_right;
> > > > -		else
> > > > +		else {
> > > > +			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
> > > > +				va, va->va_start, va->va_end, tmp_va,
> > > > +				tmp_va->va_start, tmp_va->va_end);
> > > 
> > > It might be helpful to have a "vmalloc:" prefix to that string to indicate
> > > where to start searching.  And I don't think we're supposed to use %px
> > > without a really good justification these days.
> > >
> > That makes sense, i will add such prefix for sure. As for %px i can just
> > use a casting to (unsigned long) and 0x%lx prefix.
> 
> That's not the point.  Linus wants us to not display actual pointers to
> the user.
> 
Ahh, Got it!

Then i will just remove information about addresses of two VAs.
Hope that will work.

--
Vlad Rezki