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=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 3DBEEC8302F for ; Sat, 28 Nov 2020 22:21:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 062A7222EC for ; Sat, 28 Nov 2020 22:21:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HwERhJMU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388197AbgK1Vtb (ORCPT ); Sat, 28 Nov 2020 16:49:31 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:32936 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732728AbgK1TCj (ORCPT ); Sat, 28 Nov 2020 14:02:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606590072; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=X8tIwvnAenXjgsfxToTzp4ehLsTt2g8v0KLzq8Kd0+Q=; b=HwERhJMUx34x5YHqN9lHiwhQfbIlOM1EcKOnfAhWAFL7eFyLjUzHJx7feO/b51ha63A6Rv BMeNVON7Ldws2ldCAFAuigbpFRmT+5ZXio4uMKhGrMwbjALy81FuwGqx93ST++TWSc6x1L 7FUZ6Zmq4egVdGQjEtDvvXRClogUkU8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-336-uA8Y5a2GNP-4GZ3HQXUEbA-1; Sat, 28 Nov 2020 14:01:10 -0500 X-MC-Unique: uA8Y5a2GNP-4GZ3HQXUEbA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7541E802B48; Sat, 28 Nov 2020 19:01:09 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.139]) by smtp.corp.redhat.com (Postfix) with SMTP id 9B9185D6D3; Sat, 28 Nov 2020 19:01:07 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sat, 28 Nov 2020 20:01:09 +0100 (CET) Date: Sat, 28 Nov 2020 20:01:06 +0100 From: Oleg Nesterov To: Wen Yang Cc: Alexey Dobriyan , Christian Brauner , ebiederm@xmission.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] proc: add locking checks in proc_inode_is_dead Message-ID: <20201128190105.GC19372@redhat.com> References: <20201128175850.19484-1-wenyang@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201128175850.19484-1-wenyang@linux.alibaba.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 11/29, Wen Yang wrote: > > The proc_inode_is_dead function might race with __unhash_process. > This will result in a whole bunch of stale proc entries being cached. > To prevent that, add the required locking. I leave this to Eric but I don't understand how can this patch help, __unhash_process() can be called right after proc_inode_is_dead(). And in any case, we certainly do not want to take tasklist_lock in proc_inode_is_dead(). > > Signed-off-by: Wen Yang > Cc: Oleg Nesterov > Cc: "Eric W. Biederman" > Cc: Alexey Dobriyan > Cc: Christian Brauner > Cc: linux-kernel@vger.kernel.org > Cc: linux-fsdevel@vger.kernel.org > --- > fs/proc/base.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 1bc9bcd..59720bc 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -1994,7 +1994,13 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags) > > static inline bool proc_inode_is_dead(struct inode *inode) > { > - return !proc_pid(inode)->tasks[PIDTYPE_PID].first; > + bool has_task; > + > + read_lock(&tasklist_lock); > + has_task = pid_has_task(proc_pid(inode), PIDTYPE_PID); > + read_unlock(&tasklist_lock); > + > + return !has_task; > } > > int pid_delete_dentry(const struct dentry *dentry) > -- > 1.8.3.1 >