linux-kernel - [PATCH rcu v2] 18/20] srcu: Document that srcu_{read_lock,down_read}() can share srcu

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Message-Id: <20250130190317.1652481-18-paulmck@kernel.org>
Date: Thu, 30 Jan 2025 11:03:15 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	bpf@...r.kernel.org
Subject: [PATCH rcu v2] 18/20] srcu: Document that srcu_{read_lock,down_read}() can share srcu_struct

This commit adds a sentence to the srcu_down_read() function's kernel-doc
header noting that it is permissible to use srcu_down_read() and
srcu_read_lock() on the same srcu_struct, even concurrently.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: <bpf@...r.kernel.org>
---
 include/linux/srcu.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index a0df80baaccf..317eab82a5f0 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -359,7 +359,8 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
  * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
  *
  * Calls to srcu_down_read() may be nested, similar to the manner in
- * which calls to down_read() may be nested.
+ * which calls to down_read() may be nested.  The same srcu_struct may be
+ * used concurrently by srcu_down_read() and srcu_read_lock().
  */
 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
 {
-- 
2.40.1