linux-kernel - [PATCH v4 4/5] asm-generic: barrier: Add smp_cond_load_acquire

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Message-Id: <20250829080735.3598416-5-ankur.a.arora@oracle.com>
Date: Fri, 29 Aug 2025 01:07:34 -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 v4 4/5] asm-generic: barrier: Add smp_cond_load_acquire_timewait()

Add the acquire variant of smp_cond_load_relaxed_timewait(). This
reuses the relaxed variant, with an additional LOAD->LOAD
ordering.

Cc: Arnd Bergmann <arnd@...db.de>
Cc: Will Deacon <will@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: linux-arch@...r.kernel.org
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 include/asm-generic/barrier.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index c87d6fd8746f..58e510e37b87 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -308,6 +308,28 @@ do {									\
 })
 #endif
 
+/**
+ * smp_cond_load_acquire_timewait() - (Spin) wait for cond with ACQUIRE ordering
+ * until a timeout expires.
+ *
+ * Arguments: same as smp_cond_load_relaxed_timeout().
+ *
+ * Equivalent to using smp_cond_load_acquire() on the condition variable with
+ * a timeout.
+ */
+#ifndef smp_cond_load_acquire_timewait
+#define smp_cond_load_acquire_timewait(ptr, cond_expr, time_check_expr)	\
+({									\
+	__unqual_scalar_typeof(*ptr) _val;				\
+	_val = smp_cond_load_relaxed_timewait(ptr, cond_expr,		\
+					      time_check_expr);		\
+									\
+	/* Depends on the control dependency of the wait above. */	\
+	smp_acquire__after_ctrl_dep();					\
+	(typeof(*ptr))_val;						\
+})
+#endif
+
 /*
  * pmem_wmb() ensures that all stores for which the modification
  * are written to persistent storage by preceding instructions have
-- 
2.31.1