On Thu, Nov 02, 2023 at 10:18:55AM +0800, Huacai Chen wrote: > Hi, Nathan, > > On Thu, Nov 2, 2023 at 3:55 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > > > On Wed, Nov 01, 2023 at 12:43:29PM -0700, Nathan Chancellor wrote: > > > A recent change to the optimization pipeline in LLVM reveals some > > > fragility around the inlining of LoongArch's __percpu functions, which > > > manifests as a BUILD_BUG() failure: > > > > > > In file included from kernel/sched/build_policy.c:17: > > > In file included from include/linux/sched/cputime.h:5: > > > In file included from include/linux/sched/signal.h:5: > > > In file included from include/linux/rculist.h:11: > > > In file included from include/linux/rcupdate.h:26: > > > In file included from include/linux/irqflags.h:18: > > > arch/loongarch/include/asm/percpu.h:97:3: error: call to '__compiletime_assert_51' declared with 'error' attribute: BUILD_BUG failed > > > 97 | BUILD_BUG(); > > > | ^ > > > include/linux/build_bug.h:59:21: note: expanded from macro 'BUILD_BUG' > > > 59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed") > > > | ^ > > > include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG' > > > 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) > > > | ^ > > > include/linux/compiler_types.h:425:2: note: expanded from macro 'compiletime_assert' > > > 425 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > > > | ^ > > > include/linux/compiler_types.h:413:2: note: expanded from macro '_compiletime_assert' > > > 413 | __compiletime_assert(condition, msg, prefix, suffix) > > > | ^ > > > include/linux/compiler_types.h:406:4: note: expanded from macro '__compiletime_assert' > > > 406 | prefix ## suffix(); \ > > > | ^ > > > <scratch space>:86:1: note: expanded from here > > > 86 | __compiletime_assert_51 > > > | ^ > > > 1 error generated. > > > > > > If these functions are not inlined, the BUILD_BUG() in the default case > > > cannot be eliminated since the compiler cannot prove it is never used, > > > resulting in a build failure due to the error attribute. > > > > > > Mark these functions as __always_inline so that the BUILD_BUG() only > > > triggers when the default case genuinely cannot be eliminated due to an > > > unexpected size. > > > > > > Cc: <stable@xxxxxxxxxxxxxxx> > > > Closes: https://github.com/ClangBuiltLinux/linux/issues/1955 > > > Fixes: 46859ac8af52 ("LoongArch: Add multi-processor (SMP) support") > > > Link: https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e > > > > This should have also had: > > > > Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > > > I can pick it up if I have to send a v2. > > > > > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> > > > --- > > > arch/loongarch/include/asm/percpu.h | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h > > > index b9f567e66016..8fb857ae962b 100644 > > > --- a/arch/loongarch/include/asm/percpu.h > > > +++ b/arch/loongarch/include/asm/percpu.h > > > @@ -32,7 +32,7 @@ static inline void set_my_cpu_offset(unsigned long off) > > > #define __my_cpu_offset __my_cpu_offset > > > > > > #define PERCPU_OP(op, asm_op, c_op) \ > > > -static inline unsigned long __percpu_##op(void *ptr, \ > > > +static __always_inline unsigned long __percpu_##op(void *ptr, \ > > > unsigned long val, int size) \ > > > { \ > > > unsigned long ret; \ > > > @@ -63,7 +63,7 @@ PERCPU_OP(and, and, &) > > > PERCPU_OP(or, or, |) > > > #undef PERCPU_OP > > > > > > -static inline unsigned long __percpu_read(void *ptr, int size) > > > +static __always_inline unsigned long __percpu_read(void *ptr, int size) > > > { > > > unsigned long ret; > > > > Thank you for your patch, but I think __percpu_write() and > __percpu_xchg() also need __always_inline because they also have > BUILD_BUG(). Although we don't meet problems about them, they have > potential problems in theory. Yes, you are absolutely correct! I thought I did a survey for other BUILD_BUG() locations but seems like I did not do a good job if I did :/ I will send a v2 tomorrow with those two functions changed as well. Cheers, Nathan > > > > > > --- > > > base-commit: 278be83601dd1725d4732241f066d528e160a39d > > > change-id: 20231101-loongarch-always-inline-percpu-ops-cf77c161871f > > > > > > Best regards, > > > -- > > > Nathan Chancellor <nathan@xxxxxxxxxx> > > > > >
