linux-kernel - [PATCH 2/4] asm-generic: barrier: Add smp_cond_load_acquire

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Message-Id: <20250203214911.898276-3-ankur.a.arora@oracle.com>
Date: Mon,  3 Feb 2025 13:49:09 -0800
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
Cc: arnd@...db.de, catalin.marinas@....com, will@...nel.org,
        peterz@...radead.org, mark.rutland@....com, harisokn@...zon.com,
        cl@...two.org, memxor@...il.com, zhenglifeng1@...wei.com,
        joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, Ankur Arora <ankur.a.arora@...cle.com>
Subject: [PATCH 2/4] asm-generic: barrier: Add smp_cond_load_acquire_timewait()

Add smp_cond_load_acquire_timewait(), a timed variant of
smp_cond_load_acquire(). This is useful for cases where we want
to wait on a conditional variable but want to ensure termination.

smp_cond_load_acquire_timewait() is implemented via 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: linux-arch@...r.kernel.org
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 include/asm-generic/barrier.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 31de8ed2a05e..62673ad37db2 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -321,6 +321,29 @@ do {									\
 #define smp_cond_load_relaxed_timewait  __smp_cond_load_relaxed_spinwait
 #endif
 
+/**
+ * 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
+ * @time_expr_ns: evaluates to the current time
+ * @time_limit_ns: compared against time_expr_ns
+ *
+ * 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_expr_ns,	\
+				       time_limit_ns) ({		\
+	__unqual_scalar_typeof(*ptr) _val;				\
+	_val = smp_cond_load_relaxed_timewait(ptr, cond_expr,		\
+					      time_expr_ns,		\
+					      time_limit_ns);		\
+	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