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 01B4022A805; Tue, 18 Feb 2025 20:28:33 +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=1739910514; cv=none; b=V3WLUc3CXae8YFrs+D+9Cckb5egYPHd4NlGk4e+xPznKUNkOwvLxBSmgyvJRP1chkaKIhgcoV6JoSjtsQW9xplprizoWcOmS4g2KiUY94aeDa3n5PGaCFS1/t/e1v1jt/wFIJQQiqpqVZAeuVpDcgzJiHe74cP6UcxorhueTojs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739910514; c=relaxed/simple; bh=G647sp4ARJlDgB5GswPaejJMTJPmTJIkpQpdVMHafHw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=rfB+4XczKL8m59uKQBsJloL0osw2tg83hqwcuQpX60LVKZF0V21oUJofaVLbyEeukFaKBX34RjIvyxqyPmuwgh8qtJb4FgPrtUlZ0dFt2WyzF1TLe/VscZVad6ZKbOwKz/UpnUoVAzxGDSyWkvgKxzccDttgNNPs9oId9iSVIbs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a324VSi7; 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="a324VSi7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A293DC4CEE4; Tue, 18 Feb 2025 20:28:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739910513; bh=G647sp4ARJlDgB5GswPaejJMTJPmTJIkpQpdVMHafHw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=a324VSi7w/cmLdPH2Dauvxtb9a2PYob8Vao1zLCgQmiPUVQWDPuo90gOUEnOC680k 0CnaccSKiJT8JK5fI8uLK+kdFccqzCbi78MzWTqOPaApQnx9wVayL/Z8HNciQ7GZOY niqeJQVs2e62Md6LAvgLnXZer+JZZHunDgQ60V7Dpn5NAFjZTVpbFQdyhMIqoQ5Yda U5xXOmG692oYH1zxEtQbfgxfbo+G/oLA1aASEjFhWprUGGxwKQ01by922+j+HCOUvU tmO3MwbCoUa/cRIC3uXTRtvFu1sHKZaruSXxz9KaPw5xQifcn0MsqSofQ5MX08U3v2 +S0Xj3YKTmgpg== 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 6.1 06/13] sched: Clarify wake_up_q()'s write to task->wake_q.next Date: Tue, 18 Feb 2025 15:28:10 -0500 Message-Id: <20250218202819.3593598-6-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250218202819.3593598-1-sashal@kernel.org> References: <20250218202819.3593598-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.1.128 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 54af671e8d510..83a29609d478d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -995,9 +995,10 @@ 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