This is a note to let you know that I've just added the patch titled
LoongArch: Change __my_cpu_offset definition to avoid mis-optimization
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
loongarch-change-__my_cpu_offset-definition-to-avoid.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6c02dbfb399845c9b9352a012956df306d68130c
Author: Huacai Chen <chenhuacai@xxxxxxxxxx>
Date: Tue Mar 19 15:50:34 2024 +0800
LoongArch: Change __my_cpu_offset definition to avoid mis-optimization
[ 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@xxxxxxxxxxxxxxx
Reported-by: Xiaotian Wu <wuxiaotian@xxxxxxxxxxx>
Reported-by: Miao Wang <shankerwangmiao@xxxxxxxxx>
Signed-off-by: Xing Li <lixing@xxxxxxxxxxx>
Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
Signed-off-by: Rui Wang <wangrui@xxxxxxxxxxx>
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h
index 9b36ac003f890..8f290e5546cf7 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, \
