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.
