linux-kernel - [PATCH 0/1] turn mm->exe_file into mm->exe

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Date:	Mon, 5 Mar 2012 16:28:26 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Helsley <matthltc@...ibm.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <keescook@...omium.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 0/1] turn mm->exe_file into mm->exe_path

I think the patch is simple and self-explanatory, it simply
does s/mm->exe_file/mm->exe_path/.

Why do we need mm->exe_file? IIUC, there are 2 reasons:

	1. we do not want O(n) proc/pid/exe looking for the 1st
	   VM_EXECUTABLE vma.

	2. we do not want to rely on vma->vm_file->f_path,
	   bprm->file->f_op->mmap can change ->vm_file.

Unless there was another subtle reason, "struct path *exe_path"
can equally work but it looks more clear.

And can't we also remove added_exe_file_vma/removed_exe_file_vma?
Why do we need mm->num_exe_file_vmas? Afaics it is only needed to
"free" mm->exe_file if the application unmaps all these vmas. Say,
to allow to unmount fs.

Can't we simply add PR_CLEAR_MM_EXE_PATH instead? Of course it is
not enough if ->vm_file still has a reference. But c/r people want
PR_SET_MM_EXE_FILE anyway, see http://marc.info/?t=133052865500016
So perhaps we can add PR_SET_MM_EXE_PATH which accepts NULL as well
and kill this counter?

Oleg.

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