From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19853C4338F for ; Mon, 16 Aug 2021 19:30:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E191060F4B for ; Mon, 16 Aug 2021 19:30:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229699AbhHPTbF (ORCPT ); Mon, 16 Aug 2021 15:31:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:38242 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229587AbhHPTbE (ORCPT ); Mon, 16 Aug 2021 15:31:04 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 79E5860E76; Mon, 16 Aug 2021 19:30:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1629142233; bh=DxEqcZW45zJUiMURvvvNQVHFj6LuwzgYwo1VSNLXGhY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Hvtr5MIkxxgr5073QkCcZFdDYqpdP/RHj8iXn8/QKtmkDC7594BkCEmCWN+hbf3DD h7/UH4Uv0mcnoYFaJFoCJqly8+OaS+kse4KYpsZ5W7nfQwJXR70SumjdSxfUxvcGXo h/zdWaPcJKkeQA7YAI1m4Jzl+HOapR0D+hK+xwKQ= Date: Mon, 16 Aug 2021 21:30:30 +0200 From: Greg Kroah-Hartman To: David Chen Cc: "stable@vger.kernel.org" , "Paul E. McKenney" , "neeraju@codeaurora.org" Subject: Re: Request for backport fd6bc19d7676 to 4.14 and 4.19 branch Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Aug 16, 2021 at 07:19:34PM +0000, David Chen wrote: > Hi Greg, > > We recently hit a hung task timeout issue in synchronize_rcu_expedited on 4.14 branch. > The issue seems to be identical to the one described in `fd6bc19d7676 rcu: Fix missed wakeup of exp_wq waiters` > Can we backport it to 4.14 and 4.19 branch? > The patch doesn't apply cleanly, but it should be trivial to resolve, just do this > > - wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp->expedited_sequence) & 0x3]); > + wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]); > > I don't know if we should do it for 4.9, because the handling of sequence number is a bit different. Please provide a working backport, me hand-editing patches does not scale, and this way you get the proper credit for backporting it (after testing it). You have tested, this, right? thanks, greg k-h