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 E35F21E526; Thu, 15 Aug 2024 14:21:24 +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=1723731685; cv=none; b=OsM8v14G7ILeRakchwm3Grz3nXVnMb+xtH+V6RbbEOSDqrRetxXNy7MyoJUzBRjkwpLjoUe3Zd1D8P3hUpCtz8RT8o7Z83hqKXV9deo4ohiVRsuD6eWPbkK40Vjb4Qcm8RWSlyH6oOcjFpum8kUPjoVcFnTIokyet3/l7xYN+BQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723731685; c=relaxed/simple; bh=tNWRTiVbJIvOOD77ShOke4aTU00QecqYQoSlrfRePpo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=P7ir87fa/S9y+z/1ZxVPuLKxaZeho4ElD/+a9S8b53nFJvn0q9f/ljspJPoWdC0Y59BddUNvzHVEv52j14Bwq5OfLghDoYZClPNaEcugaficA4TjgTLiCPWSXRnZjNpIJQegiiWx/0kDwYN9q+AdU4CJjaaNvfUpZwtZobNFEbM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=QGUkc8EC; 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="QGUkc8EC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5514AC32786; Thu, 15 Aug 2024 14:21:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1723731684; bh=tNWRTiVbJIvOOD77ShOke4aTU00QecqYQoSlrfRePpo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QGUkc8ECi21w/db3e0rAFt5fMxiFnkKfUkFCG3p9wSBkkVo4q3MfAg5TQ4xYOQLMH RBzfZ9CghCjotVwxQmD2G1/dGiIlmQK6+ilpbAsECp5QHj+blLKlipPZ2X67DuWydW fqV/e/5Y2VFX6ib22nsmZKAzPNRjwPKEDEs4i/CQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Benjamin Coddington , Jeff Layton , Anna Schumaker , Sasha Levin Subject: [PATCH 5.4 206/259] SUNRPC: Fix a race to wake a sync task Date: Thu, 15 Aug 2024 15:25:39 +0200 Message-ID: <20240815131910.727661644@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240815131902.779125794@linuxfoundation.org> References: <20240815131902.779125794@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ 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