From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 88FD381A for ; Fri, 25 Aug 2023 12:42:12 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 970FA1BE for ; Fri, 25 Aug 2023 05:42:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692967330; 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=U81j4kbmLIfbag5jx+rwwJ6qC54Rpz5edh2L4xFg6cA=; b=dG0X3vM68aBK+1HJ+d0pw5+wJn+oEzfm0IEa0tBGUb9N6VL9dtXcd4p0AolZZQkUHUMAvu eanwN5jwA+1H7CoKKVYfCvyIWGoV+UQo3+DVtxprRLKew0UWAEctTuUhW8uu9hmoRjnh45 nLkuNnTxCvQ7LXodAqPVro9BbrrG42I= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-589-MGReuxB9MQyyEWAJnwlT3w-1; Fri, 25 Aug 2023 08:42:05 -0400 X-MC-Unique: MGReuxB9MQyyEWAJnwlT3w-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B95A22808E61; Fri, 25 Aug 2023 12:42:04 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.225.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 025B1492C13; Fri, 25 Aug 2023 12:42:02 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 25 Aug 2023 14:41:18 +0200 (CEST) Date: Fri, 25 Aug 2023 14:41:15 +0200 From: Oleg Nesterov To: Yonghong Song , Kui-Feng Lee , Andrii Nakryiko Cc: "Eric W. Biederman" , Martin KaFai Lau , bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] bpf: task_group_seq_get_next: cleanup the usage of next_thread() Message-ID: <20230825124115.GA13849@redhat.com> References: <20230821150909.GA2431@redhat.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230821150909.GA2431@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net OK, it seems that you are not going to take these preparatory cleanups ;) I'll resend along with the s/next_thread/__next_thread/ change. I was going to do the last change later, but this recent discussion https://lore.kernel.org/all/20230824143112.GA31208@redhat.com/ makes me think we should do this right now. On 08/21, Oleg Nesterov wrote: > > 1. find_pid_ns() + get_pid_task() under rcu_read_lock() guarantees that we > can safely iterate the task->thread_group list. Even if this task exits > right after get_pid_task() (or goto retry) and pid_alive() returns 0. > > Kill the unnecessary pid_alive() check. > > 2. next_thread() simply can't return NULL, kill the bogus "if (!next_task)" > check. > > Signed-off-by: Oleg Nesterov > --- > kernel/bpf/task_iter.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c > index c4ab9d6cdbe9..4d1125108014 100644 > --- a/kernel/bpf/task_iter.c > +++ b/kernel/bpf/task_iter.c > @@ -75,15 +75,8 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > return NULL; > > retry: > - if (!pid_alive(task)) { > - put_task_struct(task); > - return NULL; > - } > - > next_task = next_thread(task); > put_task_struct(task); > - if (!next_task) > - return NULL; > > saved_tid = *tid; > *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns); > -- > 2.25.1.362.g51ebf55 > >