linux-kernel - Re: [PATCH 1/3] uprobes: install_breakpoint() should fail if is_swbp

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Date:	Fri, 1 Jun 2012 20:38:44 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] uprobes: install_breakpoint() should fail if
	is_swbp_insn() == T

On 06/01, Srikar Dronamraju wrote:
>
> * Oleg Nesterov <oleg@...hat.com> [2012-05-31 20:53:39]:
>
> > __find_next_vma_info() checks tmpvi->mm == vma->vm_mm to detect the
> > already visited mm/vma. However, afaics this can be false positive?
> >
> > The caller, register_for_each_vma(), does mmput() and after that
> > this memory can be freed and re-used as another mm_struct.
> >
>
> Before we do a mmput(), we take the mmap_sem for that mm. So this mm
> cannot be freed until we complete insertion/removal.  If the mm gets
> reused after the insertion/removal, and maps the inode,

Yes, see the previous email from me, we can rely on uprobe_mmap().

> Or are you hinting at some other problem?

Perhaps this deserves a comment. I mean, to explain that yes,
tmpvi->mm == vma->vm_mm can be wrong but this is fine.

However, I hope we simply can kill this code. See build_map_info()
I sent.

Oleg.

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