linux-kernel - vdso && f_op->mremap (Was: special_mapping

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Message-ID: <20150623004744.GA11212@redhat.com>
Date:	Tue, 23 Jun 2015 02:47:44 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Hugh Dickins <hughd@...gle.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: vdso && f_op->mremap (Was: special_mapping_fault() is broken)

On 06/21, Oleg Nesterov wrote:
>
> Forgot to add Andy...

Add Pavel ;)

I never understood why ->mremap() lives in file_operations, not in
vm_operations_struct. To me vma->vm_file->f_op in move_vma() just
looks strange, vma->vm_ops->mremap(new_vma) looks "obviously better".

And afaics more useful. CRIU remaps vdso, but this does not update
mm->context.vdso. OK, probably this does not matter currently, CRIU
can't c/r the compat tasks, and 64-bit apps do not use context.vdso.
Afaics. Still, I think we might want to have special_mapping_remap()
and we can't do this because ->vm_file == NULL.

And perhaps other architectures can depend on the "correct" value
in >context.vdso more then x86, I dunno...

In short. Shouldn't we move ->mremap() to vm_operations_struct before
it has another user? We need to fix aio.c, but this is trivial.

No?

Oleg.

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