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=-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=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 DD603C11F69 for ; Thu, 1 Jul 2021 17:24:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C48E961407 for ; Thu, 1 Jul 2021 17:24:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233269AbhGAR0u (ORCPT ); Thu, 1 Jul 2021 13:26:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232977AbhGAR0t (ORCPT ); Thu, 1 Jul 2021 13:26:49 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0395C061764 for ; Thu, 1 Jul 2021 10:24:18 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id l16-20020a25cc100000b0290558245b7eabso9653468ybf.10 for ; Thu, 01 Jul 2021 10:24:18 -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=38K6QON43H6pH2g0pIEjP7BxAKWPFxAgioG2jiQJXbo=; b=aAoFWVvB2eQX8hemEnJKLwfAYIV6KQBm9A34wD1JuIPSUnV7DCsibpNnPdcd8s8N0i xb3YvOZM/K7gNU0iG6MBhVg81Ttw2ZWaBzBcVnlpSQFw4bXFqfLHUl+VSCk+SzxKsLnl u/4QEluBiQC/pREQBRfFUV3sd6e9KnKSeXSwMdRbfLylvJPchmzdErc8pMPmm4m/J1Yz SWUPAhQSY82+bsX6yjwHvwGoqjVwspENQELDYqjXPxC4oMwFmnPoXLniHSbXeZYxdbBr qktBdLVUV7vHaVejeLAYqf/O4rxJpxqqLB3z1vWl5bOCrc08UGhz/L17sjWutmFNfqUW 3YpA== 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=38K6QON43H6pH2g0pIEjP7BxAKWPFxAgioG2jiQJXbo=; b=D15Zeu8DpVB5Cj9yJY7eo0ilGDAzSxqjMrzASpQnGlzA4umwew7LJGvsWD+tnEjimq DbIiHRhAKZr5HDIged5di4yo0IYynVvGJ2jUHqlcQbz02rcjg0jW6CmiQOL/J3ZfBGgd r0r6L9N1lCL2bbSQMnKh8V4FdpsniIcLHHVp5nz/Y5sdw9SwTl+g26xPjAb8rSHeaQL1 3IvUBz+EEwNA498tlpc0G3fMkI6h4EluW0BO5YNeEiGPESqtHT7a2bwP1ZQ3vIuAXWQi 0Qe3bkL1ECbYOEDZuGmbMM0tU3tvoNMMS/ngSMMQZ5DbhNhS8NUDpOH4N4DlFFB1afp+ 43Zg== X-Gm-Message-State: AOAM532qI4rYLPaZkahTQnXEaoid8pf9MNz8rjaJJjtCYTF+ATX0Lw9F b7XTCu5LvRwMUSxARiEbJS5TmwsIDdrQ9Kf1cir67bNMyCIRiIlGxx/9otjykMLqg7cKt2vqmsr AEzHPuSuOdH9Kc8e2UiFYt5ieZ1o5jq57G2ZdUhXJ8gy0Rsos+X2UhMPg7dV60LzH2L9a9uJUCI 6I1JUb X-Google-Smtp-Source: ABdhPJwsiZdKBSmIxnQj9cHmceY++/Ee801Kq5zF2bYouqu9kW1FVUm0/Eb2H/CgKDHLBiWuX8aiUqqWZQwyL6U2 X-Received: from paulburton.mtv.corp.google.com ([2620:15c:280:201:558a:406a:d453:dbe5]) (user=paulburton job=sendgmr) by 2002:a25:c58d:: with SMTP id v135mr1024007ybe.383.1625160257767; Thu, 01 Jul 2021 10:24:17 -0700 (PDT) Date: Thu, 1 Jul 2021 10:24:07 -0700 In-Reply-To: <20210701172407.889626-1-paulburton@google.com> Message-Id: <20210701172407.889626-2-paulburton@google.com> Mime-Version: 1.0 References: <20210701095525.400839d3@oasis.local.home> <20210701172407.889626-1-paulburton@google.com> X-Mailer: git-send-email 2.32.0.93.g670b81a890-goog Subject: [PATCH v2 2/2] tracing: Resize tgid_map to pid_max, not PID_MAX_DEFAULT From: Paul Burton To: linux-kernel@vger.kernel.org Cc: Paul Burton , Steven Rostedt , Ingo Molnar , Joel Fernandes , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently tgid_map is sized at PID_MAX_DEFAULT entries, which means that on systems where pid_max is configured higher than PID_MAX_DEFAULT the ftrace record-tgid option doesn't work so well. Any tasks with PIDs higher than PID_MAX_DEFAULT are simply not recorded in tgid_map, and don't show up in the saved_tgids file. In particular since systemd v243 & above configure pid_max to its highest possible 1<<22 value by default on 64 bit systems this renders the record-tgids option of little use. Increase the size of tgid_map to the configured pid_max instead, allowing it to cover the full range of PIDs up to the maximum value of PID_MAX_LIMIT if the system is configured that way. On 64 bit systems with pid_max == PID_MAX_LIMIT this will increase the size of tgid_map from 256KiB to 16MiB. Whilst this 64x increase in memory overhead sounds significant 64 bit systems are presumably best placed to accommodate it, and since tgid_map is only allocated when the record-tgid option is actually used presumably the user would rather it spends sufficient memory to actually record the tgids they expect. The size of tgid_map could also increase for CONFIG_BASE_SMALL=y configurations, but these seem unlikely to be systems upon which people are both configuring a large pid_max and running ftrace with record-tgid anyway. Of note is that we only allocate tgid_map once, the first time that the record-tgid option is enabled. Therefore its size is only set once, to the value of pid_max at the time the record-tgid option is first enabled. If a user increases pid_max after that point, the saved_tgids file will not contain entries for any tasks with pids beyond the earlier value of pid_max. 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: --- Changes in v2: - Use the configured value of pid_max at the time record-tgid is enabled rather than unconditionally using PID_MAX_LIMIT, to avoid added memory overhead for systems that don't configure such a high pid_max. --- kernel/trace/trace.c | 60 ++++++++++++++++++++++++++++++-------------- 1 file changed, 41 insertions(+), 19 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 7a37c9e36b88..3c4b3b207c06 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2184,8 +2184,13 @@ void tracing_reset_all_online_cpus(void) } } +// The tgid_map array maps from pid to tgid; i.e. the value stored at index i +// is the tgid last observed corresponding to pid=i. static int *tgid_map; +// The maximum valid index into tgid_map. +static size_t tgid_map_max; + #define SAVED_CMDLINES_DEFAULT 128 #define NO_CMDLINE_MAP UINT_MAX static arch_spinlock_t trace_cmdline_lock = __ARCH_SPIN_LOCK_UNLOCKED; @@ -2458,24 +2463,39 @@ void trace_find_cmdline(int pid, char comm[]) preempt_enable(); } +static int *trace_find_tgid_ptr(int pid) +{ + // Pairs with the smp_store_release in set_tracer_flag() to ensure that + // if we observe a non-NULL tgid_map then we also observe the correct + // tgid_map_max. + int *map = smp_load_acquire(&tgid_map); + + if (unlikely(!map || pid > tgid_map_max)) + return NULL; + + return &map[pid]; +} + int trace_find_tgid(int pid) { - if (unlikely(!tgid_map || !pid || pid > PID_MAX_DEFAULT)) - return 0; + int *ptr = trace_find_tgid_ptr(pid); - return tgid_map[pid]; + return ptr ? *ptr : 0; } static int trace_save_tgid(struct task_struct *tsk) { + int *ptr; + /* treat recording of idle task as a success */ if (!tsk->pid) return 1; - if (unlikely(!tgid_map || tsk->pid > PID_MAX_DEFAULT)) + ptr = trace_find_tgid_ptr(tsk->pid); + if (!ptr) return 0; - tgid_map[tsk->pid] = tsk->tgid; + *ptr = tsk->tgid; return 1; } @@ -5171,6 +5191,8 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set) int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled) { + int *map; + if ((mask == TRACE_ITER_RECORD_TGID) || (mask == TRACE_ITER_RECORD_CMD)) lockdep_assert_held(&event_mutex); @@ -5193,10 +5215,17 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled) trace_event_enable_cmd_record(enabled); if (mask == TRACE_ITER_RECORD_TGID) { - if (!tgid_map) - tgid_map = kvcalloc(PID_MAX_DEFAULT + 1, - sizeof(*tgid_map), - GFP_KERNEL); + if (!tgid_map) { + tgid_map_max = pid_max; + map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map), + GFP_KERNEL); + + // Pairs with smp_load_acquire() in + // trace_find_tgid_ptr() to ensure that if it observes + // the tgid_map we just allocated then it also observes + // the corresponding tgid_map_max value. + smp_store_release(&tgid_map, map); + } if (!tgid_map) { tr->trace_flags &= ~TRACE_ITER_RECORD_TGID; return -ENOMEM; @@ -5610,21 +5639,14 @@ static void *saved_tgids_next(struct seq_file *m, void *v, loff_t *pos) { int pid = ++(*pos); - if (pid > PID_MAX_DEFAULT) - 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]; + return trace_find_tgid_ptr(pid); } static void *saved_tgids_start(struct seq_file *m, loff_t *pos) { - if (!tgid_map || *pos > PID_MAX_DEFAULT) - return NULL; + int pid = *pos; - return &tgid_map[*pos]; + return trace_find_tgid_ptr(pid); } static void saved_tgids_stop(struct seq_file *m, void *v) -- 2.32.0.93.g670b81a890-goog