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=-20.2 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_GIT 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 EDBF0C64E64 for ; Mon, 19 Jul 2021 16:26:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D48C761166 for ; Mon, 19 Jul 2021 16:26:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236912AbhGSPqQ (ORCPT ); Mon, 19 Jul 2021 11:46:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:58232 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344543AbhGSO7u (ORCPT ); Mon, 19 Jul 2021 10:59:50 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id D6A2160241; Mon, 19 Jul 2021 15:40:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626709228; bh=N+LHaN51vzbIfD0cSh7WV3bQGaxS5dgOMOT/aHV2rnw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2aPByiCYQbD+FLaKYOw2kPoRrROnOE0DOKBCwV56ySLG38vlS0D3C9pOv0LAnvEO8 1foHZ9W3Gj7dOjop/i2PJ8uvfndrlNPnQ06c7YtcUTIVq6I3MgZm0xGAOpfXixiPqD 8L2PDDGOsh4vKrVzG6gGqsCpgh3vC37OxeD+7HwM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ingo Molnar , Joel Fernandes , Paul Burton , "Steven Rostedt (VMware)" Subject: [PATCH 4.19 301/421] tracing: Simplify & fix saved_tgids logic Date: Mon, 19 Jul 2021 16:51:52 +0200 Message-Id: <20210719144956.751010106@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210719144946.310399455@linuxfoundation.org> References: <20210719144946.310399455@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paul Burton commit b81b3e959adb107cd5b36c7dc5ba1364bbd31eb2 upstream. The tgid_map array records a mapping from pid to tgid, where the index of an entry within the array is the pid & the value stored at that index is the tgid. The saved_tgids_next() function iterates over pointers into the tgid_map array & dereferences the pointers which results in the tgid, but then it passes that dereferenced value to trace_find_tgid() which treats it as a pid & does a further lookup within the tgid_map array. It seems likely that the intent here was to skip over entries in tgid_map for which the recorded tgid is zero, but instead we end up skipping over entries for which the thread group leader hasn't yet had its own tgid recorded in tgid_map. A minimal fix would be to remove the call to trace_find_tgid, turning: if (trace_find_tgid(*ptr)) into: if (*ptr) ..but it seems like this logic can be much simpler if we simply let seq_read() iterate over the whole tgid_map array & filter out empty entries by returning SEQ_SKIP from saved_tgids_show(). Here we take that approach, removing the incorrect logic here entirely. Link: https://lkml.kernel.org/r/20210630003406.4013668-1-paulburton@google.com Fixes: d914ba37d714 ("tracing: Add support for recording tgid of tasks") Cc: Ingo Molnar Cc: Joel Fernandes Cc: Signed-off-by: Paul Burton Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.c | 38 +++++++++++++------------------------- 1 file changed, 13 insertions(+), 25 deletions(-) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4752,37 +4752,20 @@ static const struct file_operations trac static void *saved_tgids_next(struct seq_file *m, void *v, loff_t *pos) { - int *ptr = v; + int pid = ++(*pos); - if (*pos || m->count) - ptr++; - - (*pos)++; - - for (; ptr <= &tgid_map[PID_MAX_DEFAULT]; ptr++) { - if (trace_find_tgid(*ptr)) - return ptr; - } + if (pid > PID_MAX_DEFAULT) + return NULL; - return NULL; + return &tgid_map[pid]; } static void *saved_tgids_start(struct seq_file *m, loff_t *pos) { - void *v; - loff_t l = 0; - - if (!tgid_map) + if (!tgid_map || *pos > PID_MAX_DEFAULT) return NULL; - v = &tgid_map[0]; - while (l <= *pos) { - v = saved_tgids_next(m, v, &l); - if (!v) - return NULL; - } - - return v; + return &tgid_map[*pos]; } static void saved_tgids_stop(struct seq_file *m, void *v) @@ -4791,9 +4774,14 @@ static void saved_tgids_stop(struct seq_ static int saved_tgids_show(struct seq_file *m, void *v) { - int pid = (int *)v - tgid_map; + int *entry = (int *)v; + int pid = entry - tgid_map; + int tgid = *entry; + + if (tgid == 0) + return SEQ_SKIP; - seq_printf(m, "%d %d\n", pid, trace_find_tgid(pid)); + seq_printf(m, "%d %d\n", pid, tgid); return 0; }