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,URIBL_BLOCKED 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 47584C4338F for ; Tue, 17 Aug 2021 06:16:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12EC560FA0 for ; Tue, 17 Aug 2021 06:16:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234155AbhHQGQ5 (ORCPT ); Tue, 17 Aug 2021 02:16:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:57774 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233676AbhHQGQ5 (ORCPT ); Tue, 17 Aug 2021 02:16:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 64DF660F5C; Tue, 17 Aug 2021 06:16:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1629180984; bh=rIukTODKRHBI49BFyVKeyjRTgNsoIPhKluS8fDPo4fI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tjX2tSLHEdZGY0OmXv29xKI6ZmXFOQpIUO94amXD02Sjpm7RISgoL3ocC/q8lAlyf FHDusCNugkEI/ssyym2I9yKpSZIlUU7LIAK7ICMVmNncLnF9W5jkBtrCgAi4Cvg2Jz Q61nad2A2wzYQc7Q0B3A/VzGU5lWapIPZHMY92Zk= Date: Tue, 17 Aug 2021 08:16:22 +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 10:02:28PM +0000, David Chen wrote: > > > > -----Original Message----- > > From: Greg Kroah-Hartman > > Sent: Monday, August 16, 2021 12:31 PM > > 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 > > > > 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). > > Sure, appended at the end. > > > > > You have tested, this, right? > > I don't have a good repro for the original issue, so I only ran rcutorture and > some basic work load test to see if anything obvious went wrong. Ideally you would be able to also hit this without the patch on the older kernels, is this the case? thanks, greg k-h