linux-kernel - [PATCH 1/4] rcuwait: Support timeouts

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Message-Id: <20230523170927.20685-2-dave@stgolabs.net>
Date:   Tue, 23 May 2023 10:09:24 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     dan.j.williams@...el.com
Cc:     dave.jiang@...el.com, alison.schofield@...el.com,
        vishal.l.verma@...el.com, ira.weiny@...el.com,
        Jonathan.Cameron@...wei.com, fan.ni@...sung.com,
        a.manzanares@...sung.com, dave@...olabs.net,
        linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 1/4] rcuwait: Support timeouts

The rcuwait utility provides an efficient and safe single
wait/wake mechanism. It is used in situations where queued
wait is the wrong semantics, and often too bulky. For example,
cases where the wait is already done under a lock.

In the past, rcuwait has been extended to support beyond only
uninterruptible sleep, and similarly, there are users that can
benefit for the addition of timeouts.

As such, tntroduce rcuwait_wait_event_timeout(), with semantics
equivalent to calls for queued wait counterparts.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
---
 include/linux/rcuwait.h | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h
index 8052d34da782..27343424225c 100644
--- a/include/linux/rcuwait.h
+++ b/include/linux/rcuwait.h
@@ -49,9 +49,9 @@ static inline void prepare_to_rcuwait(struct rcuwait *w)
 
 extern void finish_rcuwait(struct rcuwait *w);
 
-#define rcuwait_wait_event(w, condition, state)				\
+#define ___rcuwait_wait_event(w, condition, state, ret, cmd)		\
 ({									\
-	int __ret = 0;							\
+	long __ret = ret;						\
 	prepare_to_rcuwait(w);						\
 	for (;;) {							\
 		/*							\
@@ -67,10 +67,27 @@ extern void finish_rcuwait(struct rcuwait *w);
 			break;						\
 		}							\
 									\
-		schedule();						\
+		cmd;							\
 	}								\
 	finish_rcuwait(w);						\
 	__ret;								\
 })
 
+#define rcuwait_wait_event(w, condition, state)				\
+	___rcuwait_wait_event(w, condition, state, 0, schedule())
+
+#define __rcuwait_wait_event_timeout(w, condition, state, timeout)	\
+	___rcuwait_wait_event(w, ___wait_cond_timeout(condition),	\
+			      state, timeout,				\
+			      __ret = schedule_timeout(__ret))
+
+#define rcuwait_wait_event_timeout(w, condition, state, timeout)	\
+({									\
+	long __ret = timeout;						\
+	if (!___wait_cond_timeout(condition))				\
+		__ret = __rcuwait_wait_event_timeout(w, condition,	\
+						     state, timeout);	\
+	__ret;								\
+})
+
 #endif /* _LINUX_RCUWAIT_H_ */
-- 
2.40.1