omapfb: don't annotate dss_conv_list as __initdata

Message ID 20200505140407.373983-1-arnd@arndb.de
State New
Headers show
Series
  • omapfb: don't annotate dss_conv_list as __initdata
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Commit Message

Arnd Bergmann May 5, 2020, 2:03 p.m.
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(-)

-- 
2.26.0

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Comments

Marco Elver May 5, 2020, 2:12 p.m. | #1
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

>

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Arnd Bergmann May 5, 2020, 3:07 p.m. | #2
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
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Patch

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,";