Applied to loongarch-next, thanks.

Huacai

On Thu, Nov 2, 2023 at 11:43 PM Nathan Chancellor nathan@kernel.org 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 (which the compiler is free to do even with functions marked with the standard 'inline' keyword), 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 to guarantee inlining so that the BUILD_BUG() only triggers when the default case genuinely cannot be eliminated due to an unexpected size.

Cc: stable@vger.kernel.org Closes: https://github.com/ClangBuiltLinux/linux/issues/1955 Fixes: 46859ac8af52 ("LoongArch: Add multi-processor (SMP) support") Link: https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a56... Suggested-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Nathan Chancellor nathan@kernel.org

---

Changes in v2:

• Change 'inline' to __always_inline for all functions that contain BUILD_BUG() (Huacai)
• Notate that 'inline' does not guarantee inlining in the commit message to further clarify the change to __always_inline.
• Link to v1: https://lore.kernel.org/r/20231101-loongarch-always-inline-percpu-ops-v1-1-b...

---

arch/loongarch/include/asm/percpu.h | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h index b9f567e66016..313852fba845 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;

@@ -100,7 +100,8 @@ static inline unsigned long __percpu_read(void *ptr, int size) return ret; }

-static inline void __percpu_write(void *ptr, unsigned long val, int size) +static __always_inline void __percpu_write(void *ptr, unsigned long val,

•                                      int size)
  

{ switch (size) { case 1: @@ -132,8 +133,8 @@ static inline void __percpu_write(void *ptr, unsigned long val, int size) } }

-static inline unsigned long __percpu_xchg(void *ptr, unsigned long val,

•                                           int size)
  

+static __always_inline unsigned long __percpu_xchg(void *ptr, unsigned long val,

•                                              int size)
  

{ switch (size) { case 1:

---

base-commit: 278be83601dd1725d4732241f066d528e160a39d change-id: 20231101-loongarch-always-inline-percpu-ops-cf77c161871f

Best regards,

Nathan Chancellor nathan@kernel.org