linux-kernel - Re: [RFC] [Patch 0/21] Non disruptive application core dump infrastructure

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Date:	Wed, 15 Dec 2010 10:54:11 +0530
From:	"Suzuki K. Poulose" <suzuki@...ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Christoph Hellwig <hch@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Daisuke HATAYAMA <d.hatayama@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>,
	Amerigo Wang <amwang@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] [Patch 0/21] Non disruptive application core dump
 infrastructure

On Wed, 15 Dec 2010 10:04:37 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Tue, 14 Dec 2010 15:22:59 +0530
> "Suzuki K. Poulose" <suzuki@...ibm.com> wrote:
> 
> > Hi all,
> > 
> > This is series of patches implementing an infrastructure for capturing the core 
> > of an application without disrupting its process semantics.
> > 
> > The infrastructure makes use of the freezer subsystem in kernel to freeze the 
> > threads and then collect the information to generate  the core.
> > 
> > The interface is provided by a /proc/pid/core file, reading which can give the 
> > ELF formatted core of the process with "pid". The interface supports "seek" 
> > operation on the fd, allowing the dumper to have control on the data that is 
> > being dumped. Also it allows the user to store the dump at any location.
> > 
> > The current implementation supports both native as well as the compat ELF 
> > tasks.
> > 
> > An open() call to the /proc/pid/core will try to freeze the threads in the 
> > process and the read() requests will dynamically generate the contents for the 
> > core file. The ELF header & Program Headers are stored in a kernel buffer to 
> > allow us to map the fpos to the required data section.
> > 
> > In case a thread is not frozen within a time interval, after issuing the freeze 
> > request, we fill the register state information with 0's to indicate we could 
> > not capture the data.
> > 
> > A close() would kick the threads out of the refrigerator().
> > 
> > 
> > The implementation reuses some of the existing ELF core generation code by 
> > exporting them. Some of the code common to both native and compat ELF class 
> > support has been moved to a common place, elfcore-common.c. Also some of the 
> > reusable functions, specific to the ELF class handling, has been made global, 
> > after renaming the compat version of the same.
> > 
> > We also added a new API -elf_core_copy_extra_phdrs() -for "reading" the arch 
> > specific program headers, versus the existing elf_core_write_extra_phdrs().
> > 
> > Patches 1 to 9 deals with re-arranging the ELF code to be reusable by the 
> > infrastructure.
> > 
> > Patches 10 to 21 implements the infrastructure.
> > 
> > TODO: Add support for collecting the arch specific notes, currently used only 
> > by Cell platform.
> > 
> > Please let me know your review comments / thoughts.
> > 
> 
> Your purpose of this patch is to debug an application without attaching to gdb
> or take coredump by gcore ? 

The purpose is to take the coredump in a more reliable way without affecting 
the process semantics.
> 
> IIUC, "freeze" is a bit dangerous because no one can ends the application while
> it's freezed and there is no information "it's frozen" via usaual user commands
> as 'ps' or 'top'. 
> 
> Can you add a new freeze state where the application can get SIGKILL,
> at least ? and show task's state as "frozen" in some way ? as
> task_state_array[] shows it in /proc/<pid>/status
I will investigate this approach.

Thanks
Suzuki
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