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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 17638C04AAF for ; Thu, 16 May 2019 17:45:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3B412070D for ; Thu, 16 May 2019 17:45:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558028728; bh=7Ad1p/8z33o2SK69h7i5zrn0GVnyRDS3xew09n2p3Yk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=D91VApeUMuIcKF9aosb9nsGLmW4wnJH2FLIV1FhSiDdTSa9z5VJWLqL5HPuhhuswY +4Qw+JaIwPiriObisSmeMLVn3rYXJrBS622BsSohzh0Mq062Tq0gxMtcsFGPpfU/XH GffGtjVsyi4DlDPyN5zf1thjxlgZ017nSEBzfiCM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728915AbfEPRp1 (ORCPT ); Thu, 16 May 2019 13:45:27 -0400 Received: from mail-qt1-f194.google.com ([209.85.160.194]:41238 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726441AbfEPRp1 (ORCPT ); Thu, 16 May 2019 13:45:27 -0400 Received: by mail-qt1-f194.google.com with SMTP id y22so4904850qtn.8; Thu, 16 May 2019 10:45:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=TZW9oPjKjF7UuQfNRNZlJhWogoRZGc1JB7uoqoIfv+8=; b=U+/Dsbpe3Ev8qOz5ABegg4QwYrxhkHAqm6TrtgUJZMxYDxJyKNRkrRR2BomF+w8bGA JeXPRak510vhmmzJ8bRXqpXFQtGibDSo/kyK2zYtiw+D7B7H/6Gb/lGYxPaHanLuyx5i gUYWYVTnZ5fNLpvZmPoI1/hpBdL/MlRiTGoXmomSU60h70cP2MeSUERNp3AMtK+BAXOR 753TXbfYLlPuastYz2vzgY435v4UWD/63ouWJF2lzPjL0KwD1TPbqNzSVAQQTSmrFxD3 BiH4q8vfb1Vc8YX3FlMIFhHYqPuYMeE0fF9Zpl545yER8ygpzwARFTZi9cGlYGk6xKUt f7dA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=TZW9oPjKjF7UuQfNRNZlJhWogoRZGc1JB7uoqoIfv+8=; b=rALhC8waL0mjiX2VLLZKV3UrmLDWRWQmqRXe6mxhcEVixh6aRsAoqaHuaUl381LHYi 1hMLat+r/yvLsRhbH5g4D2DX2mqV28TERoJUSbgN5RG1Gk7ZhY22mDeVVPA7FkaZNlIw gFU9vSMoQD+Lu68clyxRDzIa8qdp2uFVqxflgfkJkwRZxT8foAX+fCdyP/sLHfcO0wvX SbycO0VwzWyvFw8yX0bi7NABzVj8jIWO7IHNg3JpzsIw4Xr55/A5I91vGR9lqvpHCOO2 rqX96gSP7a4eYDfMl3Yd724ByPRRok3kNYUJcGIy/zdmPvXWrqC63QJTt7K4ZSdeBieG 7T+Q== X-Gm-Message-State: APjAAAWT0rh1A0VCPJGtUSxaRscucZqsDfCYlfeY/XZytfilYg/0iSO5 BgVB2AderhTof76oBUAccU42NqioRHg= X-Google-Smtp-Source: APXvYqyUkVz3sqfNMifhOeY7ZDSeqgmGmjvjqqsICWFuayNjL9C3yjroqXXDBYnZFz5G9EOCbhBW9Q== X-Received: by 2002:a05:6214:41:: with SMTP id c1mr33503890qvr.138.1558028725812; Thu, 16 May 2019 10:45:25 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::3:e390]) by smtp.gmail.com with ESMTPSA id e37sm4124575qte.23.2019.05.16.10.45.24 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 May 2019 10:45:24 -0700 (PDT) Date: Thu, 16 May 2019 10:45:23 -0700 From: Tejun Heo To: Roman Gushchin Cc: Oleg Nesterov , Alex Xu , kernel-team@fb.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND] signal: unconditionally leave the frozen state in ptrace_stop() Message-ID: <20190516174523.GD374014@devbig004.ftw2.facebook.com> References: <20190516173821.1498807-1-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190516173821.1498807-1-guro@fb.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 16, 2019 at 10:38:21AM -0700, Roman Gushchin wrote: > Alex Xu reported a regression in strace, caused by the introduction of > the cgroup v2 freezer. The regression can be reproduced by stracing > the following simple program: > > #include > > int main() { > write(1, "a", 1); > return 0; > } > > An attempt to run strace ./a.out leads to the infinite loop: > [ pre-main omitted ] > write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) > write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) > write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) > write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) > write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) > write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) > [ repeats forever ] > > The problem occurs because the traced task leaves ptrace_stop() > (and the signal handling loop) with the frozen bit set. So let's > call cgroup_leave_frozen(true) unconditionally after sleeping > in ptrace_stop(). > > With this patch applied, strace works as expected: > [ pre-main omitted ] > write(1, "a", 1) = 1 > exit_group(0) = ? > +++ exited with 0 +++ > > Reported-by: Alex Xu > Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer") > Signed-off-by: Roman Gushchin > Acked-by: Oleg Nesterov > Cc: Tejun Heo Applied to cgroup/for-5.2-fixes. Thanks. -- tejun