Re: [PATCH] coredump: add %T in core_pattern to report the tid
From: Oleg Nesterov
Date: Mon Sep 22 2014 - 11:25:32 EST
Self-nack after discussion on debug-list, I'll send v2.
If we teach format_corename() to report task_pid_vnr() we should also
allow to report the global tid from the root namespace, at least to
make this consistent with %p/%P.
This means that %T was a bad choice, Martin suggests %i/%I.
On 09/21, Oleg Nesterov wrote:
> 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 <jan.kratochvil@xxxxxxxxxx>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> 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.
> %<NUL> '%' 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",
> + case 'T':
> + err = cn_printf(cn, "%d",
> + task_pid_vnr(current));
> + break;
> /* global pid */
> case 'P':
> err = cn_printf(cn, "%d",
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/