From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7E49518801C; Tue, 30 Jul 2024 16:04:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722355465; cv=none; b=dgpzlXmpown/bE5Ha3YaJ5+0jhufQ+tGawQljwOge67gUtwH6YuPaGzHVZaJEzRdEZRDGj6/h/+h3oVB/HLmlFs2n+5GWmiqBbBaoKAXf0VX36pnMUlOdqd5Um7+qp41/KiWJP90OTw2Hcli1NRHWKzSeRpmeZo2K29crNP83ns= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722355465; c=relaxed/simple; bh=k5BOQjM9IJ+ljKQETDty/Ji3BtwTfGkVQHytqECe0Ls=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Tk2N2SyAsSEMG9qSfxg8z3JVXlJWAvB1JQbIobSntX29YtcA5qb3t1LaF93f2soUFBON5zenjDDa6Mt0tRwjupXEYpSuHfAJe42EGDzSq5fYGqlKfFiv0+FndickjDbL/f08P/o90mOSbEgZKW5AmCG/wOlu6Zu32zRIta4l+vM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Zqlqd0jl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Zqlqd0jl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD6D6C4AF0A; Tue, 30 Jul 2024 16:04:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1722355465; bh=k5BOQjM9IJ+ljKQETDty/Ji3BtwTfGkVQHytqECe0Ls=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Zqlqd0jlPmb/CTxaJd6LH4QtzS8x7yQ9GTHLhbUUua46oyNLXoxO4FODt7tDORjN6 QGXPUGaoAW4Cb2nhY3revJUEqMUS2FAnFNJV+FVdsB9yWyJVBX5lJLwd6cLK4tfoEI 7H4eb+rQ5XwflOZlXqrK1TXzrIUbg1RKoYfIx788= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Uros Bizjak , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.1 097/440] jump_label: Use atomic_try_cmpxchg() in static_key_slow_inc_cpuslocked() Date: Tue, 30 Jul 2024 17:45:30 +0200 Message-ID: <20240730151619.674992121@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240730151615.753688326@linuxfoundation.org> References: <20240730151615.753688326@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Uros Bizjak [ Upstream commit d0c006402e7941558e5283ae434e2847c7999378 ] Use atomic_try_cmpxchg() instead of atomic_cmpxchg (*ptr, old, new) == old in static_key_slow_inc_cpuslocked(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Signed-off-by: Uros Bizjak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20221019140850.3395-1-ubizjak@gmail.com Stable-dep-of: 83ab38ef0a0b ("jump_label: Fix concurrency issues in static_key_slow_dec()") Signed-off-by: Sasha Levin --- kernel/jump_label.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 714ac4c3b556d..4d6c6f5f60db8 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -115,8 +115,6 @@ EXPORT_SYMBOL_GPL(static_key_count); void static_key_slow_inc_cpuslocked(struct static_key *key) { - int v, v1; - STATIC_KEY_CHECK_USE(key); lockdep_assert_cpus_held(); @@ -132,11 +130,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) * so it counts as "enabled" in jump_label_update(). Note that * atomic_inc_unless_negative() checks >= 0, so roll our own. */ - for (v = atomic_read(&key->enabled); v > 0; v = v1) { - v1 = atomic_cmpxchg(&key->enabled, v, v + 1); - if (likely(v1 == v)) + for (int v = atomic_read(&key->enabled); v > 0; ) + if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))) return; - } jump_label_lock(); if (atomic_read(&key->enabled) == 0) { -- 2.43.0