[PATCH] omapfb: don't annotate dss_conv_list as __initdata

[PATCH] omapfb: don't annotate dss_conv_list as __initdata

[Arnd Bergmann]

With the kcsan changes, __read_once_size() is not inlined, but
clang can decide to emit a version that hardcodes the address, which
in turn triggers a warning for dss_conv_list being __initdata but
__read_once_size() not being __init:

WARNING: modpost: vmlinux.o(.text+0x6e4d7a): Section mismatch in
reference from the function __read_once_size() to the variable
.init.data:dss_conv_list
The function __read_once_size() references
the variable __initdata dss_conv_list.
This is often because __read_once_size lacks a __initdata
annotation or the annotation of dss_conv_list is wrong.

This is clearly a false positive warning, but it's hard to tell
who is to blame for it. Work around it by removing the __initdata
annotation, wasting the space of two pointers in return for getting
rid of the warning.

Fixes: dfd402a4c4ba ("kcsan: Add Kernel Concurrency Sanitizer infrastructure")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c b/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c
index 0ae0cab252d3..29fdff9c95f6 100644
--- a/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c
+++ b/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c
@@ -19,7 +19,7 @@
 #include <linux/slab.h>
 #include <linux/list.h>
 
-static struct list_head dss_conv_list __initdata;
+static struct list_head dss_conv_list;
 
 static const char prefix[] __initconst = "omapdss,";
 
-- 
2.26.0

Re: [PATCH] omapfb: don't annotate dss_conv_list as __initdata

[Marco Elver]

On Tue, 5 May 2020 at 16:04, Arnd Bergmann <arnd@arndb.de> wrote:
>
> With the kcsan changes, __read_once_size() is not inlined, but
> clang can decide to emit a version that hardcodes the address, which
> in turn triggers a warning for dss_conv_list being __initdata but
> __read_once_size() not being __init:
>
> WARNING: modpost: vmlinux.o(.text+0x6e4d7a): Section mismatch in
> reference from the function __read_once_size() to the variable
> .init.data:dss_conv_list
> The function __read_once_size() references
> the variable __initdata dss_conv_list.
> This is often because __read_once_size lacks a __initdata
> annotation or the annotation of dss_conv_list is wrong.
>
> This is clearly a false positive warning, but it's hard to tell
> who is to blame for it. Work around it by removing the __initdata
> annotation, wasting the space of two pointers in return for getting
> rid of the warning.
>
> Fixes: dfd402a4c4ba ("kcsan: Add Kernel Concurrency Sanitizer infrastructure")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

[+Cc Will]

I think Will is working on a series that completely overhauls
READ_ONCE/WRITE_ONCE, also getting rid of __read_once_size() in the
process, which would make this patch redundant. If we can live with
this warning until the new READ_ONCE/WRITE_ONCE gets merged, we can
probably keep things as-is for now.

Thanks,
-- Marco

> ---
>  drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c b/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c
> index 0ae0cab252d3..29fdff9c95f6 100644
> --- a/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c
> +++ b/drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c
> @@ -19,7 +19,7 @@
>  #include <linux/slab.h>
>  #include <linux/list.h>
>
> -static struct list_head dss_conv_list __initdata;
> +static struct list_head dss_conv_list;
>
>  static const char prefix[] __initconst = "omapdss,";
>
> --
> 2.26.0
>

Re: [PATCH] omapfb: don't annotate dss_conv_list as __initdata

[Arnd Bergmann]

On Tue, May 5, 2020 at 4:12 PM 'Marco Elver' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
> On Tue, 5 May 2020 at 16:04, Arnd Bergmann <arnd@arndb.de> wrote:
> > With the kcsan changes, __read_once_size() is not inlined, but
> > clang can decide to emit a version that hardcodes the address, which
> > in turn triggers a warning for dss_conv_list being __initdata but
> > __read_once_size() not being __init:
> >
> > WARNING: modpost: vmlinux.o(.text+0x6e4d7a): Section mismatch in
> > reference from the function __read_once_size() to the variable
> > .init.data:dss_conv_list
> > The function __read_once_size() references
> > the variable __initdata dss_conv_list.
> > This is often because __read_once_size lacks a __initdata
> > annotation or the annotation of dss_conv_list is wrong.
> >
> > This is clearly a false positive warning, but it's hard to tell
> > who is to blame for it. Work around it by removing the __initdata
> > annotation, wasting the space of two pointers in return for getting
> > rid of the warning.
> >
> > Fixes: dfd402a4c4ba ("kcsan: Add Kernel Concurrency Sanitizer infrastructure")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> [+Cc Will]
>
> I think Will is working on a series that completely overhauls
> READ_ONCE/WRITE_ONCE, also getting rid of __read_once_size() in the
> process, which would make this patch redundant. If we can live with
> this warning until the new READ_ONCE/WRITE_ONCE gets merged, we can
> probably keep things as-is for now.

Ok, let's drop this one for now.

        Arnd