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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 B8458C43331 for ; Fri, 3 Apr 2020 03:33:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 677AC20675 for ; Fri, 3 Apr 2020 03:33:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390358AbgDCDc7 (ORCPT ); Thu, 2 Apr 2020 23:32:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:55848 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388951AbgDCDc6 (ORCPT ); Thu, 2 Apr 2020 23:32:58 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 07C4420675; Fri, 3 Apr 2020 03:32:56 +0000 (UTC) Date: Thu, 2 Apr 2020 23:32:55 -0400 From: Steven Rostedt To: LKML Cc: Ingo Molnar , Andrew Morton , Masami Hiramatsu Subject: [PATCH][for-next] tracing: One last update before sending a pull request Message-ID: <20200402233255.1dd3a5e8@oasis.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git for-next Head SHA1: 75b564fe13f10b4ba1500c4022396b56befa489f Steven Rostedt (VMware) (1): tracing: Do not allocate buffer in trace_find_next_entry() in atomic ---- kernel/trace/trace.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) --------------------------- commit 75b564fe13f10b4ba1500c4022396b56befa489f Author: Steven Rostedt (VMware) Date: Wed Apr 1 22:44:46 2020 -0400 tracing: Do not allocate buffer in trace_find_next_entry() in atomic When dumping out the trace data in latency format, a check is made to peek at the next event to compare its timestamp to the current one, and if the delta is of a greater size, it will add a marker showing so. But to do this, it needs to save the current event otherwise peeking at the next event will remove the current event. To save the event, a temp buffer is used, and if the event is bigger than the temp buffer, the temp buffer is freed and a bigger buffer is allocated. This allocation is a problem when called in atomic context. The only way this gets called via atomic context is via ftrace_dump(). Thus, use a static buffer of 128 bytes (which covers most events), and if the event is bigger than that, simply return NULL. The callers of trace_find_next_entry() need to handle a NULL case, as that's what would happen if the allocation failed. Link: https://lore.kernel.org/r/20200326091256.GR11705@shao2-debian Fixes: ff895103a84ab ("tracing: Save off entry when peeking at next entry") Reported-by: kernel test robot Signed-off-by: Steven Rostedt (VMware) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6519b7afc499..4b7bbfe7f809 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3472,6 +3472,9 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu, return next; } +#define STATIC_TEMP_BUF_SIZE 128 +static char static_temp_buf[STATIC_TEMP_BUF_SIZE]; + /* Find the next real entry, without updating the iterator itself */ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter, int *ent_cpu, u64 *ent_ts) @@ -3480,13 +3483,26 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter, int ent_size = iter->ent_size; struct trace_entry *entry; + /* + * If called from ftrace_dump(), then the iter->temp buffer + * will be the static_temp_buf and not created from kmalloc. + * If the entry size is greater than the buffer, we can + * not save it. Just return NULL in that case. This is only + * used to add markers when two consecutive events' time + * stamps have a large delta. See trace_print_lat_context() + */ + if (iter->temp == static_temp_buf && + STATIC_TEMP_BUF_SIZE < ent_size) + return NULL; + /* * The __find_next_entry() may call peek_next_entry(), which may * call ring_buffer_peek() that may make the contents of iter->ent * undefined. Need to copy iter->ent now. */ if (iter->ent && iter->ent != iter->temp) { - if (!iter->temp || iter->temp_size < iter->ent_size) { + if ((!iter->temp || iter->temp_size < iter->ent_size) && + !WARN_ON_ONCE(iter->temp == static_temp_buf)) { kfree(iter->temp); iter->temp = kmalloc(iter->ent_size, GFP_KERNEL); if (!iter->temp) @@ -9203,6 +9219,8 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) /* Simulate the iterator */ trace_init_global_iter(&iter); + /* Can not use kmalloc for iter.temp */ + iter.temp = static_temp_buf; for_each_tracing_cpu(cpu) { atomic_inc(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);