linux-kernel - [PATCH 7/8] sched: add wait_var_event

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Message-ID: <20240925053118.3956520-8-neilb@suse.de>
Date: Wed, 25 Sep 2024 15:24:10 +1000
From: NeilBrown <neilb@...e.de>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 7/8] sched: add wait_var_event_io()

It is not currently possible to wait wait_var_event for an io_schedule()
style wait.  This patch adds wait_var_event_io() for that purpose.

Signed-off-by: NeilBrown <neilb@...e.de>
---
 include/linux/wait_bit.h | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h
index 6aea10efca3d..6346e26fbfd1 100644
--- a/include/linux/wait_bit.h
+++ b/include/linux/wait_bit.h
@@ -281,6 +281,9 @@ __out:	__ret;								\
 #define __wait_var_event(var, condition)				\
 	___wait_var_event(var, condition, TASK_UNINTERRUPTIBLE, 0, 0,	\
 			  schedule())
+#define __wait_var_event_io(var, condition)				\
+	___wait_var_event(var, condition, TASK_UNINTERRUPTIBLE, 0, 0,	\
+			  io_schedule())
 
 /**
  * wait_var_event - wait for a variable to be updated and notified
@@ -306,6 +309,34 @@ do {									\
 	__wait_var_event(var, condition);				\
 } while (0)
 
+/**
+ * wait_var_event_io - wait for a variable to be updated and notified
+ * @var: the address of variable being waited on
+ * @condition: the condition to wait for
+ *
+ * Wait for an IO related @condition to be true, only re-checking when a
+ * wake up is received for the given @var (an arbitrary kernel address
+ * which need not be directly related to the given condition, but
+ * usually is).
+ *
+ * The process will wait on a waitqueue selected by hash from a shared
+ * pool.  It will only be woken on a wake_up for the given address.
+ *
+ * This is similar to wait_var_event(), but calls io_schedule() instead
+ * of schedule().
+ *
+ * The condition should normally use smp_load_acquire() or a similarly
+ * ordered access to ensure that any changes to memory made before the
+ * condition became true will be visible after the wait completes.
+ */
+#define wait_var_event_io(var, condition)				\
+do {									\
+	might_sleep();							\
+	if (condition)							\
+		break;							\
+	__wait_var_event_io(var, condition);				\
+} while (0)
+
 #define __wait_var_event_killable(var, condition)			\
 	___wait_var_event(var, condition, TASK_KILLABLE, 0, 0,		\
 			  schedule())
-- 
2.46.0