Re: kcsan -Wmaybe-uninitialized warning in ntfs3

Marco Elver
2026-04-22T11:51:29Z

On Wed, Apr 22, 2026 at 01:35PM +0200, Marco Elver wrote:
> On Wed, 22 Apr 2026 at 10:23, Marco Elver <elver@google.com> wrote:
> >
> > On Wed, 22 Apr 2026 at 10:00, Arnd Bergmann <arnd@arndb.de> wrote:
> > >
> > > On Tue, Apr 21, 2026, at 21:12, Arnd Bergmann wrote:
> > > > On Tue, Apr 21, 2026, at 21:06, Marco Elver wrote:
> > > >> On Tue, 21 Apr 2026 at 17:26, Marco Elver <elver@google.com> wrote:
> > > >> [...]
> > > >>> > To me, 2 makes more sense. The attribute requires gcc-11 or higher,
> > > >>> > so you need to wrap that in a compiler version specific macro,
> > > >>> > but since I only saw the warning with gcc-12 and higher, that
> > > >>> > should be fine.
> > > >>
> > > >> Kindly test if you can:
> > > >> https://lore.kernel.org/all/20260421190351.1976329-1-elver@google.com/
> > > >
> > > > Applied to my randconfig tree and verified that this fixes the
> > > > known warning (only one out of about 200 random configs). I'll
> > > > let you know if something comes up by tomorrow.
> > >
> > > Unfortunately, there are new warnings after your patches using
> > > gcc-11. In 500 randconfig builds with that compiler, I saw 7
> > > configurations failing with one of these four messages:
> >
> > Looks like a compiler bug to me; can you check gcc-12+ ? Maybe we need
> > to allow the __access attribute only for later GCC versions.
>
> I can also see this warning with later GCC - so I'll give up on the
> __attribute__((access)) version and instead suppress warnings.

The simplest solution I found so far:

diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h
index 92f3843d9ebb..989fd21841ba 100644
--- a/include/linux/kcsan-checks.h
+++ b/include/linux/kcsan-checks.h
@@ -282,7 +282,7 @@ static inline void __kcsan_disable_current(void) { }
* @size: size of access
*/
#define __kcsan_check_write(ptr, size) \
- __kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
+ __kcsan_check_access(absolute_pointer(ptr), size, KCSAN_ACCESS_WRITE)

/**
* __kcsan_check_read_write - check regular read-write access for races
@@ -291,7 +291,7 @@ static inline void __kcsan_disable_current(void) { }
* @size: size of access
*/
#define __kcsan_check_read_write(ptr, size) \
- __kcsan_check_access(ptr, size, KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)
+ __kcsan_check_access(absolute_pointer(ptr), size, KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)

/**
* kcsan_check_read - check regular read access for races
@@ -308,7 +308,7 @@ static inline void __kcsan_disable_current(void) { }
* @size: size of access
*/
#define kcsan_check_write(ptr, size) \
- kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
+ kcsan_check_access(absolute_pointer(ptr), size, KCSAN_ACCESS_WRITE)

/**
* kcsan_check_read_write - check regular read-write access for races
@@ -317,7 +317,7 @@ static inline void __kcsan_disable_current(void) { }
* @size: size of access
*/
#define kcsan_check_read_write(ptr, size) \
- kcsan_check_access(ptr, size, KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)
+ kcsan_check_access(absolute_pointer(ptr), size, KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)

/*
* Check for atomic accesses: if atomic accesses are not ignored, this simply
@@ -331,9 +331,9 @@ static inline void __kcsan_disable_current(void) { }
#define kcsan_check_atomic_read(ptr, size) \
kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC)
#define kcsan_check_atomic_write(ptr, size) \
- kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE)
+ kcsan_check_access(absolute_pointer(ptr), size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE)
#define kcsan_check_atomic_read_write(ptr, size) \
- kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND)
+ kcsan_check_access(absolute_pointer(ptr), size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND)
#endif

/**