linux-kernel - [PATCH 6/8] rcu-tasks: Remove open-coded one-byte cmpxchg() emulation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241106145911.35503-7-frederic@kernel.org>
Date: Wed,  6 Nov 2024 15:59:09 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	rcu <rcu@...r.kernel.org>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 6/8] rcu-tasks: Remove open-coded one-byte cmpxchg() emulation

From: "Paul E. McKenney" <paulmck@...nel.org>

This commit removes the open-coded one-byte cmpxchg() emulation from
rcu_trc_cmpxchg_need_qs(), replacing it with just cmpxchg() given the
latter's new-found ability to handle single-byte arguments across all
architectures.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tasks.h | 17 +----------------
 1 file changed, 1 insertion(+), 16 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index dd9730fd44fb..c789d994e7eb 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1541,22 +1541,7 @@ static void rcu_st_need_qs(struct task_struct *t, u8 v)
  */
 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new)
 {
-	union rcu_special ret;
-	union rcu_special trs_old = READ_ONCE(t->trc_reader_special);
-	union rcu_special trs_new = trs_old;
-
-	if (trs_old.b.need_qs != old)
-		return trs_old.b.need_qs;
-	trs_new.b.need_qs = new;
-
-	// Although cmpxchg() appears to KCSAN to update all four bytes,
-	// only the .b.need_qs byte actually changes.
-	instrument_atomic_read_write(&t->trc_reader_special.b.need_qs,
-				     sizeof(t->trc_reader_special.b.need_qs));
-	// Avoid false-positive KCSAN failures.
-	ret.s = data_race(cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s));
-
-	return ret.b.need_qs;
+	return cmpxchg(&t->trc_reader_special.b.need_qs, old, new);
 }
 EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs);
 
-- 
2.46.0