linux-kernel - [PATCH 1/6] srcu: Add comments for srcu_size

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Message-Id: <20230315193851.8598-1-joel@joelfernandes.org>
Date:   Wed, 15 Mar 2023 19:38:46 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Zhang, Qiang1" <qiang1.zhang@...el.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org
Subject: [PATCH 1/6] srcu: Add comments for srcu_size_state

From: Pingfan Liu <kernelfans@...il.com>

The SRCU_SIZE_* names are not self-explanatory, so this commit therefore
adds comments to the definitions.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: "Zhang, Qiang1" <qiang1.zhang@...el.com>
To: rcu@...r.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 include/linux/srcutree.h | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 558057b517b7..a6910805f9c5 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -92,16 +92,29 @@ struct srcu_struct {
 	struct lockdep_map dep_map;
 };
 
-/* Values for size state variable (->srcu_size_state). */
-#define SRCU_SIZE_SMALL		0
-#define SRCU_SIZE_ALLOC		1
-#define SRCU_SIZE_WAIT_BARRIER	2
-#define SRCU_SIZE_WAIT_CALL	3
-#define SRCU_SIZE_WAIT_CBS1	4
-#define SRCU_SIZE_WAIT_CBS2	5
-#define SRCU_SIZE_WAIT_CBS3	6
-#define SRCU_SIZE_WAIT_CBS4	7
-#define SRCU_SIZE_BIG		8
+// Values for size state variable (->srcu_size_state).  Once the state
+// has been set to SRCU_SIZE_ALLOC, the grace-period code advances through
+// this state machine one step per grace period until the SRCU_SIZE_BIG state
+// is reached.  Otherwise, the state machine remains in the SRCU_SIZE_SMALL
+// state indefinitely.
+#define SRCU_SIZE_SMALL		0	// No srcu_node combining tree, ->node == NULL
+#define SRCU_SIZE_ALLOC		1	// An srcu_node tree is being allocated, initialized,
+					//  and then referenced by ->node.  It will not be used.
+#define SRCU_SIZE_WAIT_BARRIER	2	// The srcu_node tree starts being used by everything
+					//  except call_srcu(), especially by srcu_barrier().
+					//  By the end of this state, all CPUs and threads
+					//  are aware of this tree's existence.
+#define SRCU_SIZE_WAIT_CALL	3	// The srcu_node tree starts being used by call_srcu().
+					//  By the end of this state, all of the call_srcu()
+					//  invocations that were running on a non-boot CPU
+					//  and using the boot CPU's callback queue will have
+					//  completed.
+#define SRCU_SIZE_WAIT_CBS1	4	// Don't trust the ->srcu_have_cbs[] grace-period
+#define SRCU_SIZE_WAIT_CBS2	5	//  sequence elements or the ->srcu_data_have_cbs[]
+#define SRCU_SIZE_WAIT_CBS3	6	//  CPU-bitmask elements until all four elements of
+#define SRCU_SIZE_WAIT_CBS4	7	//  each array have been initialized.
+#define SRCU_SIZE_BIG		8	// The srcu_node combining tree is fully initialized
+					//  and all aspects of it are being put to use.
 
 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
-- 
2.40.0.rc1.284.g88254d51c5-goog