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 5AFF2217715; Tue, 18 Feb 2025 20:28:03 +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=1739910483; cv=none; b=DSQUdZ59BZ0RJk67SXfn6q2F5FDxYJDO3qUTISeOBULkoecej+HGBvtZtB6SX+2x807ENPTmRPzZjJayCgPlRjFtfuWD6cpKVfcJgsmG5wlNsg5N0KIjqn1XyO5O5l8Xy926uvcboAQi4NiOIUlm7C4lAEtFYTs41o11H14KGhY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739910483; c=relaxed/simple; bh=siZtmyeohjy0M7dh3zAFN17XoLrbmqH/HvLVr/ye33U=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=bxDqwF5QEjg6n/ddSN7U93wLKWJ2XxU8A6caJLCK9myWB3MF6fr7+oidbu1ilmEuo0GtM6z1UhFahjmIBvRuwCx7Fc96zNNP70HGAyTYonLAGrLaH4NajQWIud+RFqbix85LJzyiXMjB/6kbH219MnqavtWXWXyJt199KeIW1wE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=H0CNZ6Sf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="H0CNZ6Sf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5981BC4CEE9; Tue, 18 Feb 2025 20:28:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739910483; bh=siZtmyeohjy0M7dh3zAFN17XoLrbmqH/HvLVr/ye33U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=H0CNZ6SfG8jnSY0wtFUFM8xLS2L48s8/hgSCZkfArQZU4n1Cq/l+yWc68u2o7J2oF Brypw+K9X+nzn/ha/PxHr9VfKFlE50CUwVOANY1JqNZ3INTjhaw3hVT+MO1OtQZ4O2 2tHR6CmgvB6QhZzpUlbnPbyi3/hQWo5rZDfC0A/kkce9htwLXcQ7LI/FjSpzJSdpex LkHlYZveqP69CNJteZYJBvgliynBpoVF0MMzk4PIdzmiieigYCUDL8g7MBNWcxcEG0 F48XS5j30uu86D/w2hJEk/cB3kSEDqoLBjJku9dF0xiQ7OfPxMvS0XPg68eQtIBPvf J5wCm6tJDtnpQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jann Horn , Peter Zijlstra , Sasha Levin , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org Subject: [PATCH AUTOSEL 6.6 09/17] sched: Clarify wake_up_q()'s write to task->wake_q.next Date: Tue, 18 Feb 2025 15:27:33 -0500 Message-Id: <20250218202743.3593296-9-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250218202743.3593296-1-sashal@kernel.org> References: <20250218202743.3593296-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.78 Content-Transfer-Encoding: 8bit From: Jann Horn [ Upstream commit bcc6244e13b4d4903511a1ea84368abf925031c0 ] Clarify that wake_up_q() does an atomic write to task->wake_q.next, after which a concurrent __wake_q_add() can immediately overwrite task->wake_q.next again. Signed-off-by: Jann Horn Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20250129-sched-wakeup-prettier-v1-1-2f51f5f663fa@google.com Signed-off-by: Sasha Levin --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c686d826a91cf..e29746cd11afe 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1019,9 +1019,10 @@ void wake_up_q(struct wake_q_head *head) struct task_struct *task; task = container_of(node, struct task_struct, wake_q); - /* Task can safely be re-inserted now: */ node = node->next; - task->wake_q.next = NULL; + /* pairs with cmpxchg_relaxed() in __wake_q_add() */ + WRITE_ONCE(task->wake_q.next, NULL); + /* Task can safely be re-inserted now. */ /* * wake_up_process() executes a full barrier, which pairs with -- 2.39.5