On 2023/10/25 09:51, wuqiang.matt wrote:
On 2023/10/25 07:42, Masami Hiramatsu (Google) wrote:
On Tue, 24 Oct 2023 16:08:12 +0100
Mark Rutland <mark.rutl...@arm.com> wrote:
On Tue, Oct 24, 2023 at 11:52:54PM +0900, Masami Hiramatsu (Google) wrote:
From: Masami Hiramatsu (Google) <mhira...@kernel.org>
Use generic_cmpxchg_local() for arch_cmpxchg_local() implementation
in SH architecture because it does not implement arch_cmpxchg_local().
I do not think this is correct.
The implementation in <asm-generic/cmpxchg-local.h> is UP-only (and it only
disables interrupts), whereas arch/sh can be built SMP. We should probably add
some guards into <asm-generic/cmpxchg-local.h> for that as we have in
<asm-generic/cmpxchg.h>.
Isn't cmpxchg_local for the data which only needs to ensure to do cmpxchg
on local CPU?
asm-generic/cmpxchg.h is only for UP, will throw an error for SMP building:
#ifdef CONFIG_SMP
#error "Cannot use generic cmpxchg on SMP"
#endif
Sorry that I just noticed Masami's patch has asm-generic/cmpxchg-local.h
included, not asm-generic/cmpxchg.h. cmpxchg.h does throw an error for SMP
configs, but cmpxchg-local.h doesn't.
SH arch seems it does have SMP systems. The arch/sh/include/asm/cmpxchg.h has
the following codes:
#if defined(CONFIG_GUSA_RB)
#include <asm/cmpxchg-grb.h>
#elif defined(CONFIG_CPU_SH4A)
#include <asm/cmpxchg-llsc.h>
#elif defined(CONFIG_CPU_J2) && defined(CONFIG_SMP)
#include <asm/cmpxchg-cas.h>
#else
#include <asm/cmpxchg-irq.h>
#endif
So I think it doesn't care about the other CPUs (IOW, it should not touched by
other CPUs), so it only considers UP case. E.g. on x86, arch_cmpxchg_local() is
defined as raw "cmpxchg" without lock prefix.
#define __cmpxchg_local(ptr, old, new, size) \
__raw_cmpxchg((ptr), (old), (new), (size), "")
Thank you,
I think the right thing to do here is to define arch_cmpxchg_local() in terms
of arch_cmpxchg(), i.e. at the bottom of arch/sh's <asm/cmpxchg.h> add:
#define arch_cmpxchg_local arch_cmpxchg
I agree too. Might not be performance optimized but guarantees correctness.
Mark.
Reported-by: kernel test robot <l...@intel.com>
Closes:
https://lore.kernel.org/oe-kbuild-all/202310241310.ir5uukog-...@intel.com/
Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
arch/sh/include/asm/cmpxchg.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h
index 288f6f38d98f..e920e61fb817 100644
--- a/arch/sh/include/asm/cmpxchg.h
+++ b/arch/sh/include/asm/cmpxchg.h
@@ -71,4 +71,6 @@ static inline unsigned long __cmpxchg(volatile void *
ptr, unsigned long old,
(unsigned long)_n_, sizeof(*(ptr))); \
})
+#include <asm-generic/cmpxchg-local.h>
+
#endif /* __ASM_SH_CMPXCHG_H */
