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 135DC19F462; Thu, 15 Aug 2024 13:35:50 +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=1723728950; cv=none; b=U/89pBRH2Ec3MTmceD3sYX9rFIxJ9QvwwSrRwBIFs8ROtziUi0zFtO5hgkPU/nJRPb7fdcgTnTNJv91yw4h6rpPw/LjAXeoPtVsr02lt0NBjcoRWcYq7KstNkoUYy6EvIE9MHlUO293JiOSyZRKDNMQwWrckpJEpndIh+r3YeIs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723728950; c=relaxed/simple; bh=a1Ho4/PFE0gK/5iXg1Wj/SebUPkcMGNyvTFntVc8OOs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BWF72ZseeKAQIswVMa+oa6Snra6od+/rLl/TW+IlLneWWv+8bZch/5vfpvNmlEP67X/MgpNf7t2We4oWjR/cVVX+neO7yztKtaLmVOJtuKb8H2H7cqDz5IDuiCsfvO1NeU+sJMbb5kbwBTBqbDdQNdln8JYF+VbdmdCVuSQa4M8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jahEl1pa; 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="jahEl1pa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7988BC4AF0A; Thu, 15 Aug 2024 13:35:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1723728950; bh=a1Ho4/PFE0gK/5iXg1Wj/SebUPkcMGNyvTFntVc8OOs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jahEl1paMVWuqXQFv7fVMO3IPONEHZMziNtlkus4m1vdXPH6YM3c4sEV3C+707tjH CYG5vsAIjbSqi2/VIh6GNj0holc7CH35BiV3a4GdnLgW88HAbczWgX0hp+mbKUuKrK Cnnu1kTfU/PTfYZwb0cGiWAPw3O2+qJfr0a4M1vY= 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 4.19 145/196] SUNRPC: Fix a race to wake a sync task Date: Thu, 15 Aug 2024 15:24:22 +0200 Message-ID: <20240815131857.621369970@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240815131852.063866671@linuxfoundation.org> References: <20240815131852.063866671@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 4.19-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 9af919364a001..92d88aa62085b 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -349,8 +349,10 @@ 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