[PATCH 6.6 173/396] LoongArch: Change __my_cpu_offset definition to avoid mis-optimization

Greg Kroah-Hartman
2024-04-01T16:44:17Z

From: Huacai Chen <chenhuacai@loongson.cn>

[ Upstream commit c87e12e0e8c1241410e758e181ca6bf23efa5b5b ]

>From GCC commit 3f13154553f8546a ("df-scan: remove ad-hoc handling of
global regs in asms"), global registers will no longer be forced to add
to the def-use chain. Then current_thread_info(), current_stack_pointer
and __my_cpu_offset may be lifted out of the loop because they are no
longer treated as "volatile variables".

This optimization is still correct for the current_thread_info() and
current_stack_pointer usages because they are associated to a thread.
However it is wrong for __my_cpu_offset because it is associated to a
CPU rather than a thread: if the thread migrates to a different CPU in
the loop, __my_cpu_offset should be changed.

Change __my_cpu_offset definition to treat it as a "volatile variable",
in order to avoid such a mis-optimization.

Cc: stable@vger.kernel.org
Reported-by: Xiaotian Wu <wuxiaotian@loongson.cn>
Reported-by: Miao Wang <shankerwangmiao@gmail.com>
Signed-off-by: Xing Li <lixing@loongson.cn>
Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
Signed-off-by: Rui Wang <wangrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/loongarch/include/asm/percpu.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h
index ed5da02b1cf6f..7e804140500f1 100644
--- a/arch/loongarch/include/asm/percpu.h
+++ b/arch/loongarch/include/asm/percpu.h
@@ -29,7 +29,12 @@ static inline void set_my_cpu_offset(unsigned long off)
__my_cpu_offset = off;
csr_write64(off, PERCPU_BASE_KS);
}
-#define __my_cpu_offset __my_cpu_offset
+
+#define __my_cpu_offset \
+({ \
+ __asm__ __volatile__("":"+r"(__my_cpu_offset)); \
+ __my_cpu_offset; \
+})

#define PERCPU_OP(op, asm_op, c_op) \
static __always_inline unsigned long __percpu_##op(void *ptr, \
--
2.43.0