From patchwork Thu Jul 1 17:24:06 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Burton X-Patchwork-Id: 469486 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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, 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,USER_IN_DEF_DKIM_WL 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 BAAF5C11F64 for ; Thu, 1 Jul 2021 17:24:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 903CE61407 for ; Thu, 1 Jul 2021 17:24:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233119AbhGAR0p (ORCPT ); Thu, 1 Jul 2021 13:26:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233045AbhGAR0p (ORCPT ); Thu, 1 Jul 2021 13:26:45 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49556C061762 for ; Thu, 1 Jul 2021 10:24:14 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id v184-20020a257ac10000b02904f84a5c5297so9631740ybc.16 for ; Thu, 01 Jul 2021 10:24:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=W+yNXXd/sg5bPnMG2widlIL5j/blFdFa+1fW6PCvTrY=; b=Bhfx27LQ0RjZ0y8IYfAXVvXGTR4DzeM+8nLGds/UaofotENeKPUTQCxkK47YTSnf/q HZ5DWFhZQm8E1S1GP0987jeT2DZDblhWqmL0xsApweZRVdBg2aOhl/lE0tknIpfEX+om AZ+8woXC6FLAffO+mgr344d+UIu8XdkQ2RbQuAol84DEs9FcOa53Xq6XsXoxlD3Ej790 4JER2lVCiHR6Xw2+V/ZWDAVr2XGpMq2dsKgrzNOHDHbaaK/y2TzmqWk8lxCXrtdW7qkz DiZEO6d0uLWLprV38Pb9mc/p8UIwcOVbGV005Esz7nFpzL/fwscRKJyUa4Y913JRBF3F ElKw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=W+yNXXd/sg5bPnMG2widlIL5j/blFdFa+1fW6PCvTrY=; b=U29OZjMfk3pnhLTl6Hr3k0wzANR0d62A+NQoOYIh9KUqEaVXfGrGy6YMpjIpfWMV4P eeUxBedtG2xkRwQTQe3r1x1yXj5h+83Xy1rWJB4yWSh3E6MZY20GdLWPxAXZhoA4zY2Z mJFQG/tiy+YtZqUctokF8OFjpZMf9wnHm+63De+uHuqVY9Wr7InAGjgpY9xXZqMK7JKe NIF8k6nnXyzDS52zINA/hNFFNb+LGL+PFGNzIrkMvPYFbDxPyQ0GmeO3yKf0YAvA34Md mZRqk+QaMHYi4nLw8NpO5FPH6Caz5TKM3nrgwI8DWkbD8APU44r+rK6A77GvwB7bYr50 EWfA== X-Gm-Message-State: AOAM530gsDUYRot8o9uxmOV6O6Hy/lf7XilMWXDxtCREB7/X4QRdmYe/ qDqjfnapnV+Q5ieLkEtC4+PwypGz489y7aBp X-Google-Smtp-Source: ABdhPJyz7zVQc6WT9tGwAUSqYMLpintRtDgSOaOx3pqUXRNAodmPXxTpYoG+FPVO9E9Fb2d/4z1tud7OxUX/wY6+ X-Received: from paulburton.mtv.corp.google.com ([2620:15c:280:201:558a:406a:d453:dbe5]) (user=paulburton job=sendgmr) by 2002:a25:a225:: with SMTP id b34mr1015554ybi.485.1625160253483; Thu, 01 Jul 2021 10:24:13 -0700 (PDT) Date: Thu, 1 Jul 2021 10:24:06 -0700 In-Reply-To: <20210701095525.400839d3@oasis.local.home> Message-Id: <20210701172407.889626-1-paulburton@google.com> Mime-Version: 1.0 References: <20210701095525.400839d3@oasis.local.home> X-Mailer: git-send-email 2.32.0.93.g670b81a890-goog Subject: [PATCH v2 1/2] tracing: Simplify & fix saved_tgids logic From: Paul Burton To: linux-kernel@vger.kernel.org Cc: Paul Burton , Steven Rostedt , Ingo Molnar , Joel Fernandes , stable@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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. Signed-off-by: Paul Burton Fixes: d914ba37d714 ("tracing: Add support for recording tgid of tasks") Cc: Steven Rostedt Cc: Ingo Molnar Cc: Joel Fernandes Cc: Reviewed-by: Joel Fernandes (Google) --- Changes in v2: - Add comments describing why we know tgid_map is non-NULL in saved_tgids_next() & saved_tgids_start(). --- kernel/trace/trace.c | 45 ++++++++++++++++++++------------------------ 1 file changed, 20 insertions(+), 25 deletions(-) base-commit: 62fb9874f5da54fdb243003b386128037319b219 diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index d23a09d3eb37..7a37c9e36b88 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5608,37 +5608,23 @@ static const struct file_operations tracing_readme_fops = { 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; + // We already know that tgid_map is non-NULL here because the v + // argument is by definition a non-NULL pointer into tgid_map returned + // by saved_tgids_start() or an earlier call to saved_tgids_next(). + 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) @@ -5647,9 +5633,18 @@ static void saved_tgids_stop(struct seq_file *m, void *v) static int saved_tgids_show(struct seq_file *m, void *v) { - int pid = (int *)v - tgid_map; + int *entry = (int *)v; + int pid, tgid; + + // We already know that tgid_map is non-NULL here because the v + // argument is by definition a non-NULL pointer into tgid_map returned + // by saved_tgids_start() or saved_tgids_next(). + pid = entry - tgid_map; + 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; }