linux-kernel - [PATCH v2 3/7] arm64: barrier: enable waiting in smp_cond_load_relaxed

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Message-Id: <20250502085223.1316925-4-ankur.a.arora@oracle.com>
Date: Fri,  2 May 2025 01:52:19 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, bpf@...r.kernel.org
Cc: arnd@...db.de, catalin.marinas@....com, will@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org, mark.rutland@....com,
        harisokn@...zon.com, cl@...two.org, ast@...nel.org, memxor@...il.com,
        zhenglifeng1@...wei.com, xueshuai@...ux.alibaba.com,
        joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com
Subject: [PATCH v2 3/7] arm64: barrier: enable waiting in smp_cond_load_relaxed_timewait()

Define __smp_timewait_store() to support waiting in
smp_cond_load_relaxed_timewait(). This uses __cmpwait_relaxed() to
wait in WFE for stores to the target address, with the event-stream
periodically ensuring that we don't wait forever in the failure
case.

In the unlikely case the event-stream is unavailable, the wait_policy
is expected to just fallback to the generic spin-wait implementation.

Cc: Will Deacon <will@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 arch/arm64/include/asm/barrier.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 1ca947d5c939..eaeb78dd48c0 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -216,6 +216,9 @@ do {									\
 	(typeof(*ptr))VAL;						\
 })
 
+#define __smp_timewait_store(ptr, val)		\
+		__cmpwait_relaxed(ptr, val)
+
 #include <asm-generic/barrier.h>
 
 #endif	/* __ASSEMBLY__ */
-- 
2.43.5