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@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... Signed-off-by: Nathan Chancellor nathan@kernel.org --- 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;
--- base-commit: 278be83601dd1725d4732241f066d528e160a39d change-id: 20231101-loongarch-always-inline-percpu-ops-cf77c161871f
Best regards,
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@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...
This should have also had:
Suggested-by: Nick Desaulniers ndesaulniers@google.com
I can pick it up if I have to send a v2.
Signed-off-by: Nathan Chancellor nathan@kernel.org
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;
base-commit: 278be83601dd1725d4732241f066d528e160a39d change-id: 20231101-loongarch-always-inline-percpu-ops-cf77c161871f
Best regards,
Nathan Chancellor nathan@kernel.org
Hi, Nathan,
On Thu, Nov 2, 2023 at 3:55 AM Nathan Chancellor nathan@kernel.org 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@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...
This should have also had:
Suggested-by: Nick Desaulniers ndesaulniers@google.com
I can pick it up if I have to send a v2.
Signed-off-by: Nathan Chancellor nathan@kernel.org
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.
Huacai
base-commit: 278be83601dd1725d4732241f066d528e160a39d change-id: 20231101-loongarch-always-inline-percpu-ops-cf77c161871f
Best regards,
Nathan Chancellor nathan@kernel.org
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@kernel.org 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@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...
This should have also had:
Suggested-by: Nick Desaulniers ndesaulniers@google.com
I can pick it up if I have to send a v2.
Signed-off-by: Nathan Chancellor nathan@kernel.org
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@kernel.org
linux-stable-mirror@lists.linaro.org
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Huacai Chen -
Nathan Chancellor