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

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Date:	Tue, 20 Feb 2007 18:45:15 +0900
From:	"Kawai, Hidehiro" <hidehiro.kawai.ez@...achi.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...l.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, Robin Holt <holt@....com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	sugita <yumiko.sugita.yf@...achi.com>,
	Satoshi OSHIMA <soshima@...hat.com>,
	"Hideo AOKI@...hat" <haoki@...hat.com>
Subject: Re: [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared
    memory

Hi,

Thank you for your comments.

David Howells wrote:

>> static int elf_fdpic_dump_segments(struct file *file, struct mm_struct *mm,
>>-				   size_t *size, unsigned long *limit)
>>+				   size_t *size, unsigned long *limit,
>>+				   unsigned int omit_anon_shared)
> 
> Why are you passing it as an extra argument when you could just use
> mm->coredump_omit_anon_shared here:
> 
>>+		if (!maydump(vma, omit_anon_shared))

> I wouldn't worry, were I you, about the setting changing whilst it's being
> used.  If you are worried about that, you can probably do some locking against
> that.

Core dumping is separated two phases, one is the phase of writing
headers, the other is the phase of writing memory segments.  If the
coredump_omit_anon_shared setting is changed between these two phases,
a corrupted core file will be generated because the offsets written
in headers don't match their bodies.  So we need to use the same
setting in both phases.

I think that locking makes codes complex and generates overhead.
So I wouldn't like to use lock as far as possible.  I think passing
the flag as an extra argument is the simplest implementation to
avoid the core file corruption.

Thanks,
-- 
Hidehiro Kawai
Hitachi, Ltd., Systems Development Laboratory

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