linux-kernel - [PATCH v2 6/7] asm-generic: barrier: add smp_cond_load_acquire

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Message-Id: <20250502085223.1316925-7-ankur.a.arora@oracle.com>
Date: Fri,  2 May 2025 01:52:22 -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 6/7] 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 the additional LOAD->LOAD
ordering via smp_acquire__after_ctrl_dep().

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: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: linux-arch@...r.kernel.org
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 include/asm-generic/barrier.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 76124683be4b..2d52dc5b82fe 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -397,6 +397,32 @@ static inline u64 ___cond_spinwait(u64 now, u64 prev, u64 end,
 	(typeof(*ptr))_val;						\
 })
 
+/**
+ * smp_cond_load_acquire_timewait() - (Spin) wait for cond with ACQUIRE ordering
+ * until a timeout expires.
+ * @ptr: pointer to the variable to wait on
+ * @cond: boolean expression to wait for
+ * @wait_policy: policy handler that adjusts how much we spin before evaluating
+ *  the timeout, and if we drop into a wait for cacheline to change (depending
+ *  on architecture support.)
+ * @time_expr: monotonic expression that evaluates to the current time
+ * @time_end: compared against time_expr
+ *
+ * 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, wait_policy,	\
+				       time_expr, time_end) ({		\
+	__unqual_scalar_typeof(*ptr) _val;				\
+	_val = smp_cond_load_relaxed_timewait(ptr, cond_expr,		\
+					      wait_policy, time_expr,	\
+					      time_end);		\
+	/* 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
-- 
2.43.5