linux-kernel - Re: RFD: Non-Disruptive Core Dump Infrastructure

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Date:	Thu, 12 Sep 2013 10:15:37 +0530
From:	"Suzuki K. Poulose" <suzuki@...ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	Janani Venkataraman <jananive@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Daisuke HATAYAMA <d.hatayama@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...k.frob.com>,
	Amerigo Wang <amwang@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>, xemul@...allels.com,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	avagin@...nvz.org, gorcunov@...nvz.org,
	James Hogan <james.hogan@...tec.com>,
	Mike Frysinger <vapier@...too.org>,
	"Randy.Dunlap" <rdunlap@...otime.net>,
	Eric Paris <eparis@...hat.com>, ananth@...ibm.com,
	aravinda@...ux.vnet.ibm.com, tarundeep.singh@...ibm.com
Subject: Re: RFD: Non-Disruptive Core Dump Infrastructure

On 09/12/2013 12:57 AM, KOSAKI Motohiro wrote:
> (9/3/13 4:39 AM), Janani Venkataraman wrote:
>> Hello,
>>
>> We are working on an infrastructure to create a system core file of a
>> specific
>> process at run-time, non-disruptively. It can also be extended to a
>> case where
>> a process is able to take a self-core dump.
>>
>> gcore, an existing utility creates a core image of the specified
>> process. It
>> attaches to the process using gdb and runs the gdb gcore command and then
>> detaches. In gcore the dump cannot be issued from a signal handler
>> context as
>> fork() is not signal safe and moreover it is disruptive in nature as
>> the gdb
>> attaches using ptrace which sends a SIGSTOP signal. Hence the gcore
>> method
>> cannot be used if the process wants to initiate a self dump.
> 
> Maybe I'm missing something. But why gcore uses c-level fork()? gcore
> need to
> call pthread-at-fork handler? No. gcore need to flush stdio buffer? No.
> 
Let me clarify. If an application wants to dump itself, it has to do a
fork() and then exec the gcore with the pid of the appication to
generate the dump.

So, if the application wants to initiate the dump from a signal handler
context, it may lead to trouble.

Thanks
Suzuki

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