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. Thanks Uros!
