From b03023ecbdb76c1dec86b41ed80b123c22783220 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 13 Oct 2014 15:53:35 -0700 Subject: coredump: add %i/%I in core_pattern to report the tid of the crashed thread 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. Unfortunately %t is already used so this patch uses %i/%I. Automatic Bug Reporting Tool (https://github.com/abrt/abrt/wiki/overview) is experimenting with this. It is using the elfutils (https://fedorahosted.org/elfutils/) unwinder for generating the backtraces. Apart from not needing matching executables as mentioned above, another advantage is that we can get the backtrace without saving the core (which might be quite large) to disk. [mmilata@redhat.com: final paragraph of changelog] Signed-off-by: Jan Kratochvil Signed-off-by: Oleg Nesterov Cc: Alexander Viro Cc: Denys Vlasenko Cc: Jan Kratochvil Cc: Mark Wielaard Cc: Martin Milata Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/sysctl/kernel.txt | 2 ++ fs/coredump.c | 8 ++++++++ 2 files changed, 10 insertions(+) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index f79eb966637..57baff5bdb8 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -190,6 +190,8 @@ core_pattern is used to specify a core dumpfile pattern name. %% output one '%' %p pid %P global pid (init PID namespace) + %i tid + %I global tid (init PID namespace) %u uid %g gid %d dump mode, matches PR_SET_DUMPABLE and diff --git a/fs/coredump.c b/fs/coredump.c index a93f7e6ea4c..b5c86ffd503 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -199,6 +199,14 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm) err = cn_printf(cn, "%d", task_tgid_nr(current)); break; + case 'i': + err = cn_printf(cn, "%d", + task_pid_vnr(current)); + break; + case 'I': + err = cn_printf(cn, "%d", + task_pid_nr(current)); + break; /* uid */ case 'u': err = cn_printf(cn, "%d", cred->uid); -- cgit v1.2.3-70-g09d2