linux-kernel - [PATCH] sched: Assert for_each

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Date:   Mon, 21 Aug 2023 14:44:28 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org,
        Tong Tiangen <tongtiangen@...wei.com>, rcu@...r.kernel.org
Subject: [PATCH] sched: Assert for_each_thread() is properly locked

list_for_each_entry_rcu() takes an optional fourth argument which
allows RCU to assert that the correct lock is held.  Several callers
of for_each_thread() rely on their caller to be holding the appropriate
lock, so this is a useful assertion to include.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 include/linux/sched/signal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 669e8cff40c7..f1eae7f53be9 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -659,7 +659,8 @@ extern bool current_is_single_threaded(void);
 	while ((t = next_thread(t)) != g)
 
 #define __for_each_thread(signal, t)	\
-	list_for_each_entry_rcu(t, &(signal)->thread_head, thread_node)
+	list_for_each_entry_rcu(t, &(signal)->thread_head, thread_node, \
+		lockdep_is_held(&tasklist_lock))
 
 #define for_each_thread(p, t)		\
 	__for_each_thread((p)->signal, t)
-- 
2.40.1