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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 71EADC55192 for ; Fri, 24 Apr 2020 03:32:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47EB62073A for ; Fri, 24 Apr 2020 03:32:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587699124; bh=I1OlM/2njVJD71o/KXJZlf3QxL9rXUikbasofOdfxns=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=fB3fLPHQ63LpBviWFpwlcbWin9BizVP9UqKeRCh5A7XdGKe3NBZjbF1lwkoG76byR wodiuZHdmzlPDjSCluwdWiCRNMbtXyijDkxNZnWioDnGrUH0zwJn9W8EBd2+qIhNK3 hnaMQuO+tKVbk/FF3cKFNItaX29hsI4lhKE5b/E0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726032AbgDXDcA (ORCPT ); Thu, 23 Apr 2020 23:32:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:41670 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725922AbgDXDcA (ORCPT ); Thu, 23 Apr 2020 23:32:00 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F400020715; Fri, 24 Apr 2020 03:31:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587699120; bh=I1OlM/2njVJD71o/KXJZlf3QxL9rXUikbasofOdfxns=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=XSnyfLHvDk/uvkzKgUL1mO83yO7io8HhDylhJG07G2Zc42huWNJb4hBUHXhCNsgPe T+0Nuj6seqgc4KBmaCI7A50LRbLpQfjg9xiL9q4GNENySn+tPxP8lNo+H3a1Ea3Ko7 sYKsE1vkJHmGNY0SfDDOs3oiZx2xF2/vWwGOWOj4= Date: Thu, 23 Apr 2020 20:31:59 -0700 From: Andrew Morton To: Khazhismel Kumykov Cc: viro@zeniv.linux.org.uk, rpenyaev@suse.de, r@hev.cc, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jason Baron Subject: Re: [PATCH] eventpoll: fix missing wakeup for ovflist in ep_poll_callback Message-Id: <20200423203159.c9fc9988649e08d59e13e64d@linux-foundation.org> In-Reply-To: <20200424025057.118641-1-khazhy@google.com> References: <20200424025057.118641-1-khazhy@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, 23 Apr 2020 19:50:57 -0700 Khazhismel Kumykov wrote: > In the event that we add to ovflist, before 339ddb53d373 we would be > woken up by ep_scan_ready_list, and did no wakeup in ep_poll_callback. > With that wakeup removed, if we add to ovflist here, we may never wake > up. Rather than adding back the ep_scan_ready_list wakeup - which was > resulting un uncessary wakeups, trigger a wake-up in ep_poll_callback. > > We noticed that one of our workloads was missing wakeups starting with > 339ddb53d373 and upon manual inspection, this wakeup seemed missing to > me. With this patch added, we no longer see missing wakeups. I haven't > yet tried to make a small reproducer, but the existing kselftests in > filesystem/epoll passed for me with this patch. I'm no longer familiar with this code, so I'll await input from others. > Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll") > Signed-off-by: Khazhismel Kumykov However it sounds like a cc:stable would be warranted here, so that earlier affected kernels get the fix?