[PATCH v12 06/15] asm-generic: barrier: Add smp_cond_load_acquire_timeout()

[Ankur Arora]

Add the acquire variant of smp_cond_load_relaxed_timeout(). This
reuses the relaxed variant, with additional LOAD->LOAD ordering
via smp_acquire__after_ctrl_dep().

To ensure that the necessary control dependency on the dereference
of @ptr exists (which does not in the timeout path), introduce
an empty evaluation of the cond_expr branch.

Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Will Deacon <will at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: linux-arch at vger.kernel.org
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
Reviewed-by: Haris Okanovic <harisokn at amazon.com>
Tested-by: Haris Okanovic <harisokn at amazon.com>
Signed-off-by: Ankur Arora <ankur.a.arora at oracle.com>
---

Notes:

Sashiko notes [1] that there's a missed control dependency in the
timeout path. Fix that by forcing evaluation of the cond_expr branch.

Catalin, Haris: I've kept your R-by on this. Please let me know if
you aren't okay with this change.

[1] https://sashiko.dev/#/patchset/20260408122538.3610871-1-ankur.a.arora%40oracle.com
---
 include/asm-generic/barrier.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index c56df9513a08..0ab26e98842c 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -342,6 +342,34 @@ do {									\
 })
 #endif
 
+/**
+ * smp_cond_load_acquire_timeout() - (Spin) wait for cond with ACQUIRE ordering
+ * until a timeout expires.
+ * @ptr: pointer to the variable to wait on.
+ * @cond_expr: boolean expression to wait for.
+ * @time_expr_ns: monotonic expression that evaluates to time in ns or,
+ *  on failure, returns a negative value.
+ * @timeout_ns: timeout value in ns
+ * (Both of the above are assumed to be compatible with s64.)
+ *
+ * Equivalent to using smp_cond_load_acquire() on the condition variable with
+ * a timeout.
+ */
+#ifndef smp_cond_load_acquire_timeout
+#define smp_cond_load_acquire_timeout(ptr, cond_expr,			\
+				      time_expr_ns, timeout_ns)		\
+({									\
+	__unqual_scalar_typeof(*(ptr)) VAL;				\
+	VAL = smp_cond_load_relaxed_timeout(ptr, cond_expr,		\
+					     time_expr_ns,		\
+					     timeout_ns);		\
+	if (cond_expr)							\
+		barrier();						\
+	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