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 347D51862B4; Sun, 28 Jul 2024 15:51:00 +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=1722181860; cv=none; b=j7C9fsTcmMm7jwQ9TE1ep7jyzHQtO7A32UjB3vpPhEF/1FHkwkmapy64MA6nw/k/7r1SmikRWUaisWW6CRl6h6F36e/nKQOxPaeFcqnV3fOdOnbCF/pJUXlhqG6qhNrK+aP0ghYt+EMNw1H3Gu1ACnuHEAZdn9yys4o/BkCUANM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722181860; c=relaxed/simple; bh=a7nhMQniC6d10qzvJKZZvj5y8Afd7AHY7Dq8/OGStE8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XPcpZFYdnSjruKnf9tb2Pj+xEKJ3ocJt8d5d8yUV7HkRuur/g3Yp4aLrdkmjwzo9duCbnF9gmoWqRxYk6cO0LfJtMCeAfIzsBlnWU+cpDiLBGQxBt8XUWNLOpRxqwOOVIEX6DF0lFYKGOVhAkg/bwltRWBThg50F/Zf+ah9dbBg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=duVuOdqK; 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="duVuOdqK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 44BABC4AF0A; Sun, 28 Jul 2024 15:50:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722181860; bh=a7nhMQniC6d10qzvJKZZvj5y8Afd7AHY7Dq8/OGStE8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=duVuOdqKzOomYzXqgNmaUnEDvQXK1r9JsdequWQAkwCh9b3rDXLWwMBIr0AM2Gpb4 RXyfUexGnxuNtyES8XNpiHivB+koUIvgT7BCzYQERlWfBHqffasA5fffR/0kylCk1G E7cmmh+MK/0X4o+fX+I9u4e3tV1Z34jQDYUxMMII0NKcJdl7zTHpiLsTUVo3NWQbtE WMjOJt1L63OMrsVdxd1Fk4Z/tlzXknaf+4gCxqtayVtZuxCMOodJuVQ9PEBXUybEx+ Mb4oFrZ7ZUYD5qeRBeRpMTaYRJU3wSWduXrqDVyQq/Paby1MF8QL/V01zlGJ6Q6hU0 YCeDZqk5AyipA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Benjamin Coddington , Jeff Layton , Anna Schumaker , Sasha Levin , trondmy@kernel.org, anna@kernel.org, chuck.lever@oracle.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, linux-nfs@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH AUTOSEL 5.4 6/6] SUNRPC: Fix a race to wake a sync task Date: Sun, 28 Jul 2024 11:50:38 -0400 Message-ID: <20240728155045.2050587-6-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240728155045.2050587-1-sashal@kernel.org> References: <20240728155045.2050587-1-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 5.4.281 Content-Transfer-Encoding: 8bit From: Benjamin Coddington [ Upstream commit ed0172af5d6fc07d1b40ca82f5ca3979300369f7 ] We've observed NFS clients with sync tasks sleeping in __rpc_execute waiting on RPC_TASK_QUEUED that have not responded to a wake-up from rpc_make_runnable(). I suspect this problem usually goes unnoticed, because on a busy client the task will eventually be re-awoken by another task completion or xprt event. However, if the state manager is draining the slot table, a sync task missing a wake-up can result in a hung client. We've been able to prove that the waker in rpc_make_runnable() successfully calls wake_up_bit() (ie- there's no race to tk_runstate), but the wake_up_bit() call fails to wake the waiter. I suspect the waker is missing the load of the bit's wait_queue_head, so waitqueue_active() is false. There are some very helpful comments about this problem above wake_up_bit(), prepare_to_wait(), and waitqueue_active(). Fix this by inserting smp_mb__after_atomic() before the wake_up_bit(), which pairs with prepare_to_wait() calling set_current_state(). Signed-off-by: Benjamin Coddington Reviewed-by: Jeff Layton Signed-off-by: Anna Schumaker Signed-off-by: Sasha Levin --- net/sunrpc/sched.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index a5c6a3d05741a..df83c59cde7fe 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -368,8 +368,10 @@ static void rpc_make_runnable(struct workqueue_struct *wq, if (RPC_IS_ASYNC(task)) { INIT_WORK(&task->u.tk_work, rpc_async_schedule); queue_work(wq, &task->u.tk_work); - } else + } else { + smp_mb__after_atomic(); wake_up_bit(&task->tk_runstate, RPC_TASK_QUEUED); + } } /* -- 2.43.0