From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753386AbaIXKdy (ORCPT ); Wed, 24 Sep 2014 06:33:54 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:44081 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752792AbaIXKdX (ORCPT ); Wed, 24 Sep 2014 06:33:23 -0400 From: Daniel Thompson To: Steven Rostedt , Ingo Molnar Cc: Daniel Thompson , linux-kernel@vger.kernel.org, patches@linaro.org, linaro-kernel@lists.linaro.org, John Stultz , Sumit Semwal , kgdb-bugreport@lists.sourceforge.net, Jason Wessel Subject: [PATCH 3.17-rc4 v2 2/2] trace: kdb: Fix kernel livelock with empty buffers Date: Wed, 24 Sep 2014 11:33:01 +0100 Message-Id: <1411554781-16751-3-git-send-email-daniel.thompson@linaro.org> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1411554781-16751-1-git-send-email-daniel.thompson@linaro.org> References: <1410360247-13791-1-git-send-email-daniel.thompson@linaro.org> <1411554781-16751-1-git-send-email-daniel.thompson@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently kdb's ftdump command will livelock by constantly printk'ing the empty string at KERN_EMERG level if it run when the ftrace system is not in use. This occurs because trace_empty() never returns false when the ring buffers are left at the start of a non-consuming read [launched by ring_buffer_read_start()]. This patch changes the loop exit condition to use the result of trace_find_next_entry_inc(). Effectively this switches the non-consuming kdb dumper to follow the approach of the non-consuming userspace interface [s_next()] rather than the consuming ftrace_dump(). Signed-off-by: Daniel Thompson Cc: Jason Wessel Cc: Steven Rostedt Cc: Ingo Molnar --- kernel/trace/trace_kdb.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c index 8faa7ce..b0b1c44 100644 --- a/kernel/trace/trace_kdb.c +++ b/kernel/trace/trace_kdb.c @@ -59,19 +59,19 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file) ring_buffer_read_start(iter.buffer_iter[cpu_file]); tracing_iter_reset(&iter, cpu_file); } - if (!trace_empty(&iter)) - trace_find_next_entry_inc(&iter); - while (!trace_empty(&iter)) { + + while (trace_find_next_entry_inc(&iter)) { if (!cnt) kdb_printf("---------------------------------\n"); cnt++; - if (trace_find_next_entry_inc(&iter) != NULL && !skip_lines) + if (!skip_lines) { print_trace_line(&iter); - if (!skip_lines) trace_printk_seq(&iter.seq); - else + } else { skip_lines--; + } + if (KDB_FLAG(CMD_INTERRUPT)) goto out; } -- 1.9.3