From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752277AbaIUR4n (ORCPT ); Sun, 21 Sep 2014 13:56:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38590 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752000AbaIUR43 (ORCPT ); Sun, 21 Sep 2014 13:56:29 -0400 Date: Sun, 21 Sep 2014 19:53:49 +0200 From: Oleg Nesterov To: Andrew Morton Cc: Alexander Viro , Denys Vlasenko , Jan Kratochvil , Mark Wielaard , Martin Milata , linux-kernel@vger.kernel.org Subject: [PATCH] coredump: add %T in core_pattern to report the tid Message-ID: <20140921175349.GA21585@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org format_corename() can only pass the leader's pid to the core handler, but there is no simple way to figure out which thread originated the coredump. As Jan explains, this also means that there is no simple way to create the backtrace of the crashed process: As programs are mostly compiled with implicit gcc -fomit-frame-pointer one needs program's .eh_frame section (equivalently PT_GNU_EH_FRAME segment) or .debug_frame section. .debug_frame usually is present only in separate debug info files usually not even installed on the system. While .eh_frame is a part of the executable/library (and it is even always mapped for C++ exceptions unwinding) it no longer has to be present anywhere on the disk as the program could be upgraded in the meantime and the running instance has its executable file already unlinked from disk. One possibility is to echo 0x3f >/proc/*/coredump_filter and dump all the file-backed memory including the executable's .eh_frame section. But that can create huge core files, for example even due to mmapped data files. Other possibility would be to read .eh_frame from /proc/PID/mem at the core_pattern handler time of the core dump. For the backtrace one needs to read the register state first which can be done from core_pattern handler: ptrace(PTRACE_SEIZE, tid, 0, PTRACE_O_TRACEEXIT) close(0); // close pipe fd to resume the sleeping dumper waitpid(); // should report EXIT PTRACE_GETREGS or other requests The remaining problem is how to get the 'tid' value of the crashed thread. It could be read from the first NT_PRSTATUS note of the core file but that makes the core_pattern handler complicated. Signed-off-by: Jan Kratochvil Signed-off-by: Oleg Nesterov --- Documentation/sysctl/kernel.txt | 1 + fs/coredump.c | 4 ++++ 2 files changed, 5 insertions(+), 0 deletions(-) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index f79eb96..d2aa7f1 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -189,6 +189,7 @@ core_pattern is used to specify a core dumpfile pattern name. % '%' is dropped %% output one '%' %p pid + %T tid %P global pid (init PID namespace) %u uid %g gid diff --git a/fs/coredump.c b/fs/coredump.c index a93f7e6..1dc6106 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -194,6 +194,10 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm) err = cn_printf(cn, "%d", task_tgid_vnr(current)); break; + case 'T': + err = cn_printf(cn, "%d", + task_pid_vnr(current)); + break; /* global pid */ case 'P': err = cn_printf(cn, "%d", -- 1.5.5.1