| Message ID | 20180528155432.2864616-1-arnd@arndb.de |
|---|---|
| State | New |
| Headers | show |
| Series | dm: writecache: fix format string warning | expand |
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.
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 >
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"))) \
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
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;
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(-) -- 2.9.0