Re: [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory

From: Robin Holt <holt@sgi.com>
To: David Howells <dhowells@redhat.com>
Cc: "Kawai, Hidehiro" <hidehiro.kawai.ez@hitachi.com>,
	Andrew Morton <akpm@osdl.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	Pavel Machek <pavel@ucw.cz>, Robin Holt <holt@sgi.com>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
	sugita <yumiko.sugita.yf@hitachi.com>,
	Satoshi OSHIMA <soshima@redhat.com>,
	"Hideo AOKI@redhat" <haoki@redhat.com>
Subject: Re: [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory
Date: Wed, 21 Feb 2007 05:54:36 -0600	[thread overview]
Message-ID: <20070221115436.GA31332@lnx-holt.americas.sgi.com> (raw)
In-Reply-To: <8347.1172057611@redhat.com>

On Wed, Feb 21, 2007 at 11:33:31AM +0000, David Howells wrote:
> Kawai, Hidehiro <hidehiro.kawai.ez@hitachi.com> wrote:
> 
> > Is coredump_setting_sem a global semaphore?  If so, it prevents concurrent
> > core dumping.
> 
> No, it doesn't.  Look again:
> 
> 	int do_coredump(long signr, int exit_code, struct pt_regs * regs)
> 	{
> 		<setup vars>
> 
>  >>>>		down_read(&coredump_settings_sem);
> 
> > Additionally, while some process is dumped, writing to
> > coredump_omit_anon_shared of unrelated process will be blocked.
> 
> Yes, but that's probably reasonable.  How likely (a) is a process to coredump,
> and (b) is a coredump to occur simultaneously with someone altering their
> settings?

And (c) altering the setting during a core dump going to produce an
unusable core dump.  I don't think the locking is that difficult to add
and it just makes sense.  I would venture a guess that it will take less
time to actually do the locking than to continue arguing it is not needed
when it clearly appears it is needed for even a small number of cases.

Thanks,
Robin