On Wed, Dec 18, 2024 at 9:46 AM Gal Pressman <gal@xxxxxxxxxx> wrote: > > On 18/12/2024 10:40, Uros Bizjak wrote: > > On Wed, Dec 18, 2024 at 8:54 AM Gal Pressman <gal@xxxxxxxxxx> wrote: > >> > >> On 21/10/2024 11:07, Uros Bizjak wrote: > >>> Cast pointer from percpu address space to generic (kernel) address > >>> space in PERCPU_PTR() macro via unsigned long intermediate cast [1]. > >>> This intermediate cast is also required to avoid build failure > >>> when GCC's strict named address space checks for x86 targets [2] > >>> are enabled. > >>> > >>> Found by GCC's named address space checks. > >>> > >>> [1] https://sparse.docs.kernel.org/en/latest/annotations.html#address-space-name > >>> [2] https://gcc.gnu.org/onlinedocs/gcc/Named-Address-Spaces.html#x86-Named-Address-Spaces > >>> > >>> Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> > >>> Cc: Dennis Zhou <dennis@xxxxxxxxxx> > >>> Cc: Tejun Heo <tj@xxxxxxxxxx> > >>> Cc: Christoph Lameter <cl@xxxxxxxxx> > >>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >>> --- > >>> include/linux/percpu-defs.h | 5 ++++- > >>> 1 file changed, 4 insertions(+), 1 deletion(-) > >>> > >>> diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h > >>> index e1cf7982424f..35842d1e3879 100644 > >>> --- a/include/linux/percpu-defs.h > >>> +++ b/include/linux/percpu-defs.h > >>> @@ -221,7 +221,10 @@ do { \ > >>> } while (0) > >>> > >>> #define PERCPU_PTR(__p) \ > >>> - (typeof(*(__p)) __force __kernel *)(__p); > >>> +({ \ > >>> + unsigned long __pcpu_ptr = (__force unsigned long)(__p); \ > >>> + (typeof(*(__p)) __force __kernel *)(__pcpu_ptr); \ > >>> +}) > >>> > >>> #ifdef CONFIG_SMP > >>> > >> > >> Hello Uros, > >> > >> We've encountered a kernel panic on boot [1] bisected to this patch. > >> I believe the patch is fine and the issue is caused by a compiler bug. > >> The panic reproduces when compiling the kernel with gcc 11.3.1, but does > >> not reproduce with latest gcc/clang. > >> > >> I have a patch that workarounds the issue by ditching the intermediate > >> variable and does the casting in a single line. Will that be enough to > >> solve the sparse/build issues? > > > > Yes, single line like: > > > > (typeof(*(__p)) __force __kernel *)(__force unsigned long)(__pcpu_ptr); > > > > should be OK. > > > > Thanks, > > Uros. > > Awesome, I'll submit a patch unless I hear any objections. Please note that this is/was a preparation patch for further changes, applied to akpm's mm branch (typeof() -> TYPEOF_UNQUAL()). I'll take care to forward-port your patch to mm branch. AFAICS, the issue triggers only when KASAN is enabled. Thanks, Uros.
