Date: Wed, 15 Dec 2010 10:04:37 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: "Suzuki K. Poulose" <suzuki@in.ibm.com>
Cc: linux-kernel@vger.kernel.org,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Christoph Hellwig <hch@lst.de>, Masami Hiramatsu <mhiramat@redhat.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Daisuke HATAYAMA <d.hatayama@jp.fujitsu.com>,
        Andi Kleen <andi@firstfloor.org>, Roland McGrath <roland@redhat.com>,
        Amerigo Wang <amwang@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC] [Patch 0/21] Non disruptive application core dump
 infrastructure
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On Tue, 14 Dec 2010 15:22:59 +0530
"Suzuki K. Poulose" <suzuki@in.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 ? 

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

Thanks,
-Kame


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