[PATCH] dm: writecache: fix format string warning

[PATCH] dm: writecache: fix format string warning

[Arnd Bergmann]

The return type of ACCESS_ONCE is configuration dependent and may be either
'int' or 'long int' for the writecache_has_error() macro, so we get a warning
like this for either format string:

In file included from drivers/md/dm-writecache.c:8:
drivers/md/dm-writecache.c: In function 'writecache_status':
drivers/md/dm-writecache.c:2227:10: error: format '%ld' expects argument of type 'long int', but argument 4 has type 'int' [-Werror=format=]
   DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
          ^~~~~~~~~~~~~~~~~~~~
include/linux/device-mapper.h:549:46: note: in definition of macro 'DMEMIT'
      0 : scnprintf(result + sz, maxlen - sz, x))
                                              ^

The code is otherwise correct, so we just need to shut up the warning,
which can be done using an extra type cast.

Fixes: bb15b431d650 ("dm: add writecache target")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/md/dm-writecache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index 1ef06e738eb6..772ac3a57287 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -2224,7 +2224,7 @@ static void writecache_status(struct dm_target *ti, status_type_t type,
 
 	switch (type) {
 	case STATUSTYPE_INFO:
-		DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
+		DMEMIT("%ld %llu %llu %llu", (long)writecache_has_error(wc),
 		       (unsigned long long)wc->n_blocks, (unsigned long long)wc->freelist_size,
 		       (unsigned long long)wc->writeback_size);
 		break;
-- 
2.9.0

Re: dm: writecache: fix format string warning

[Mike Snitzer]

On Mon, May 28 2018 at 11:54am -0400,
Arnd Bergmann <arnd@arndb.de> wrote:

> The return type of ACCESS_ONCE is configuration dependent and may be either
> 'int' or 'long int' for the writecache_has_error() macro, so we get a warning
> like this for either format string:
> 
> In file included from drivers/md/dm-writecache.c:8:
> drivers/md/dm-writecache.c: In function 'writecache_status':
> drivers/md/dm-writecache.c:2227:10: error: format '%ld' expects argument of type 'long int', but argument 4 has type 'int' [-Werror=format=]
>    DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
>           ^~~~~~~~~~~~~~~~~~~~
> include/linux/device-mapper.h:549:46: note: in definition of macro 'DMEMIT'
>       0 : scnprintf(result + sz, maxlen - sz, x))
>                                               ^
> 
> The code is otherwise correct, so we just need to shut up the warning,
> which can be done using an extra type cast.
> 
> Fixes: bb15b431d650 ("dm: add writecache target")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks, I've picked this up.

Re: [PATCH] dm: writecache: fix format string warning

[Mikulas Patocka]

On Mon, 28 May 2018, Arnd Bergmann wrote:

> The return type of ACCESS_ONCE is configuration dependent and may be either
> 'int' or 'long int' for the writecache_has_error() macro, so we get a warning
> like this for either format string:

__builtin_expect returns always long, see the GCC documentation (it used 
to return int in very old gcc versions such as 2.96).

I think this is a bug in the macro __branch_check__. The variable ______r 
should be long, but it is int. This bug may cause misbehavior of other 
kernel parts (i.e. truncation of long value to int), so it should be fixed 
in __branch_check__ - not in dm-writecache.

Mikulas

> In file included from drivers/md/dm-writecache.c:8:
> drivers/md/dm-writecache.c: In function 'writecache_status':
> drivers/md/dm-writecache.c:2227:10: error: format '%ld' expects argument of type 'long int', but argument 4 has type 'int' [-Werror=format=]
>    DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
>           ^~~~~~~~~~~~~~~~~~~~
> include/linux/device-mapper.h:549:46: note: in definition of macro 'DMEMIT'
>       0 : scnprintf(result + sz, maxlen - sz, x))
>                                               ^
> 
> The code is otherwise correct, so we just need to shut up the warning,
> which can be done using an extra type cast.
> 
> Fixes: bb15b431d650 ("dm: add writecache target")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/md/dm-writecache.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> index 1ef06e738eb6..772ac3a57287 100644
> --- a/drivers/md/dm-writecache.c
> +++ b/drivers/md/dm-writecache.c
> @@ -2224,7 +2224,7 @@ static void writecache_status(struct dm_target *ti, status_type_t type,
>  
>  	switch (type) {
>  	case STATUSTYPE_INFO:
> -		DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
> +		DMEMIT("%ld %llu %llu %llu", (long)writecache_has_error(wc),
>  		       (unsigned long long)wc->n_blocks, (unsigned long long)wc->freelist_size,
>  		       (unsigned long long)wc->writeback_size);
>  		break;
> -- 
> 2.9.0
> 

[PATCH] branch-check: fix long->int truncation when profiling branches

[Mikulas Patocka]

The function __builtin_expect returns long type (see the gcc
documentation), and so do macros likely and unlikely. Unfortunatelly, when
CONFIG_PROFILE_ANNOTATED_BRANCHES is selected, the macros likely and
unlikely expand to __branch_check__ and __branch_check__ truncates the
long type to int. This unintended truncation may cause bugs in various
kernel code (we found a bug in dm-writecache because of it), so it's
better to fix __branch_check__ to return long.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

---
 include/linux/compiler.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/include/linux/compiler.h
===================================================================
--- linux-2.6.orig/include/linux/compiler.h	2018-02-26 20:34:17.000000000 +0100
+++ linux-2.6/include/linux/compiler.h	2018-05-30 14:11:53.000000000 +0200
@@ -21,7 +21,7 @@ void ftrace_likely_update(struct ftrace_
 #define unlikely_notrace(x)	__builtin_expect(!!(x), 0)
 
 #define __branch_check__(x, expect, is_constant) ({			\
-			int ______r;					\
+			long ______r;					\
 			static struct ftrace_likely_data		\
 				__attribute__((__aligned__(4)))		\
 				__attribute__((section("_ftrace_annotated_branch"))) \

Re: [PATCH] branch-check: fix long->int truncation when profiling branches

[Steven Rostedt]

On Wed, 30 May 2018 08:19:22 -0400 (EDT)
Mikulas Patocka <mpatocka@redhat.com> wrote:

> The function __builtin_expect returns long type (see the gcc
> documentation), and so do macros likely and unlikely. Unfortunatelly, when
> CONFIG_PROFILE_ANNOTATED_BRANCHES is selected, the macros likely and
> unlikely expand to __branch_check__ and __branch_check__ truncates the

Nice catch.

> long type to int. This unintended truncation may cause bugs in various
> kernel code (we found a bug in dm-writecache because of it), so it's

I'm curious to what that bug was.

> better to fix __branch_check__ to return long.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org

Anyway, I can pull this in my tree and test it.

-- Steve

> 
> ---
>  include/linux/compiler.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/include/linux/compiler.h
> ===================================================================
> --- linux-2.6.orig/include/linux/compiler.h	2018-02-26 20:34:17.000000000 +0100
> +++ linux-2.6/include/linux/compiler.h	2018-05-30 14:11:53.000000000 +0200
> @@ -21,7 +21,7 @@ void ftrace_likely_update(struct ftrace_
>  #define unlikely_notrace(x)	__builtin_expect(!!(x), 0)
>  
>  #define __branch_check__(x, expect, is_constant) ({			\
> -			int ______r;					\
> +			long ______r;					\
>  			static struct ftrace_likely_data		\
>  				__attribute__((__aligned__(4)))		\
>  				__attribute__((section("_ftrace_annotated_branch"))) \

Re: [PATCH] branch-check: fix long->int truncation when profiling branches

[Mikulas Patocka]

On Mon, 4 Jun 2018, Steven Rostedt wrote:

> On Wed, 30 May 2018 08:19:22 -0400 (EDT)
> Mikulas Patocka <mpatocka@redhat.com> wrote:
> 
> > The function __builtin_expect returns long type (see the gcc
> > documentation), and so do macros likely and unlikely. Unfortunatelly, when
> > CONFIG_PROFILE_ANNOTATED_BRANCHES is selected, the macros likely and
> > unlikely expand to __branch_check__ and __branch_check__ truncates the
> 
> Nice catch.
> 
> > long type to int. This unintended truncation may cause bugs in various
> > kernel code (we found a bug in dm-writecache because of it), so it's
> 
> I'm curious to what that bug was.

printk("%ld", writecache_has_error(wc))

... and writecache_has_error was defined as
#define writecache_has_error(wc)	(unlikely(READ_ONCE((wc)->error)))

Mikulas