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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 E6960C43381 for ; Wed, 27 Mar 2019 18:25:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B1C912177E for ; Wed, 27 Mar 2019 18:25:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553711130; bh=u7JrxVM2Qj3OnqH/5zUWHJRX+hA3aA2UhfXhYgA1vg4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=HTB/lJRODPGUgKcJjJlxH4yj3sMDCq4FOacmq1aCwexJidbaAs81UoXfQZAidwzP9 tGX1jM0FKfiQErXRNJCDvl60GGgrI02At3F31XE7uUmImqZr86/oQt6lZP+gIZ6uZJ bz+sCbi+Mti57XqwOXMB4KLpWZJktv484CwXn8oA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404207AbfC0SZ3 (ORCPT ); Wed, 27 Mar 2019 14:25:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:44422 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404173AbfC0SZY (ORCPT ); Wed, 27 Mar 2019 14:25:24 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A5FA9206BA; Wed, 27 Mar 2019 18:25:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553711123; bh=u7JrxVM2Qj3OnqH/5zUWHJRX+hA3aA2UhfXhYgA1vg4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GE/cFKJ8tTP7+E9Vre/3uZ6UiiGiADPzsfrFXngySlYSQEzxcpMiuz93AkSJR9pWi cEIfJ56x/Vs0RJ6oIZQm1hra4dsKx4pnAae7dYrc9UeeUp6zGzXAyvHSzaivTQvka6 YpPxmdfqPan3y8LqZULAZ4ZCs1j4yqziW6fIL8kU= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Douglas Anderson , Steven Rostedt , Sasha Levin Subject: [PATCH AUTOSEL 3.18 02/41] tracing: kdb: Fix ftdump to not sleep Date: Wed, 27 Mar 2019 14:24:39 -0400 Message-Id: <20190327182518.19394-2-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190327182518.19394-1-sashal@kernel.org> References: <20190327182518.19394-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Douglas Anderson [ Upstream commit 31b265b3baaf55f209229888b7ffea523ddab366 ] As reported back in 2016-11 [1], the "ftdump" kdb command triggers a BUG for "sleeping function called from invalid context". kdb's "ftdump" command wants to call ring_buffer_read_prepare() in atomic context. A very simple solution for this is to add allocation flags to ring_buffer_read_prepare() so kdb can call it without triggering the allocation error. This patch does that. Note that in the original email thread about this, it was suggested that perhaps the solution for kdb was to either preallocate the buffer ahead of time or create our own iterator. I'm hoping that this alternative of adding allocation flags to ring_buffer_read_prepare() can be considered since it means I don't need to duplicate more of the core trace code into "trace_kdb.c" (for either creating my own iterator or re-preparing a ring allocator whose memory was already allocated). NOTE: another option for kdb is to actually figure out how to make it reuse the existing ftrace_dump() function and totally eliminate the duplication. This sounds very appealing and actually works (the "sr z" command can be seen to properly dump the ftrace buffer). The downside here is that ftrace_dump() fully consumes the trace buffer. Unless that is changed I'd rather not use it because it means "ftdump | grep xyz" won't be very useful to search the ftrace buffer since it will throw away the whole trace on the first grep. A future patch to dump only the last few lines of the buffer will also be hard to implement. [1] https://lkml.kernel.org/r/20161117191605.GA21459@google.com Link: http://lkml.kernel.org/r/20190308193205.213659-1-dianders@chromium.org Reported-by: Brian Norris Signed-off-by: Douglas Anderson Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Sasha Levin --- include/linux/ring_buffer.h | 2 +- kernel/trace/ring_buffer.c | 5 +++-- kernel/trace/trace.c | 6 ++++-- kernel/trace/trace_kdb.c | 6 ++++-- 4 files changed, 12 insertions(+), 7 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 4daa5069cbdb..561f79803c13 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -125,7 +125,7 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts, unsigned long *lost_events); struct ring_buffer_iter * -ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu); +ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags); void ring_buffer_read_prepare_sync(void); void ring_buffer_read_start(struct ring_buffer_iter *iter); void ring_buffer_read_finish(struct ring_buffer_iter *iter); diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index d2b609412c3a..173ff025ea75 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4039,6 +4039,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_consume); * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer * @buffer: The ring buffer to read from * @cpu: The cpu buffer to iterate over + * @flags: gfp flags to use for memory allocation * * This performs the initial preparations necessary to iterate * through the buffer. Memory is allocated, buffer recording @@ -4056,7 +4057,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_consume); * This overall must be paired with ring_buffer_read_finish. */ struct ring_buffer_iter * -ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu) +ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_iter *iter; @@ -4064,7 +4065,7 @@ ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu) if (!cpumask_test_cpu(cpu, buffer->cpumask)) return NULL; - iter = kmalloc(sizeof(*iter), GFP_KERNEL); + iter = kmalloc(sizeof(*iter), flags); if (!iter) return NULL; diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 69af9a1b1031..934c1a1813dd 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3047,7 +3047,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) if (iter->cpu_file == RING_BUFFER_ALL_CPUS) { for_each_tracing_cpu(cpu) { iter->buffer_iter[cpu] = - ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu); + ring_buffer_read_prepare(iter->trace_buffer->buffer, + cpu, GFP_KERNEL); } ring_buffer_read_prepare_sync(); for_each_tracing_cpu(cpu) { @@ -3057,7 +3058,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) } else { cpu = iter->cpu_file; iter->buffer_iter[cpu] = - ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu); + ring_buffer_read_prepare(iter->trace_buffer->buffer, + cpu, GFP_KERNEL); ring_buffer_read_prepare_sync(); ring_buffer_read_start(iter->buffer_iter[cpu]); tracing_iter_reset(iter, cpu); diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c index bd90e1b06088..ebbf28492573 100644 --- a/kernel/trace/trace_kdb.c +++ b/kernel/trace/trace_kdb.c @@ -46,14 +46,16 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file) if (cpu_file == RING_BUFFER_ALL_CPUS) { for_each_tracing_cpu(cpu) { iter.buffer_iter[cpu] = - ring_buffer_read_prepare(iter.trace_buffer->buffer, cpu); + ring_buffer_read_prepare(iter.trace_buffer->buffer, + cpu, GFP_ATOMIC); ring_buffer_read_start(iter.buffer_iter[cpu]); tracing_iter_reset(&iter, cpu); } } else { iter.cpu_file = cpu_file; iter.buffer_iter[cpu_file] = - ring_buffer_read_prepare(iter.trace_buffer->buffer, cpu_file); + ring_buffer_read_prepare(iter.trace_buffer->buffer, + cpu_file, GFP_ATOMIC); ring_buffer_read_start(iter.buffer_iter[cpu_file]); tracing_iter_reset(&iter, cpu_file); } -- 2.19.1