linux-kernel - Re: [PATCH 5/7] uprobes: introduce MMF_HAS

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Date:	Mon, 13 Aug 2012 18:52:21 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] uprobes: introduce MMF_HAS_UPROBES

* Oleg Nesterov <oleg@...hat.com> [2012-08-08 19:37:47]:

> Add the new MMF_HAS_UPROBES flag. It is set by install_breakpoint()
> and it is copied by dup_mmap(), uprobe_pre_sstep_notifier() checks
> it to avoid the slow path if the task was never probed. Perhaps it
> makes sense to check it in valid_vma(is_register => false) as well.
> 
> This needs the new dup_mmap()->uprobe_dup_mmap() hook. We can't use
> uprobe_reset_state() or put MMF_HAS_UPROBES into MMF_INIT_MASK, we
> need oldmm->mmap_sem to avoid the race with uprobe_register() or
> mmap() from another thread.
> 
> Currently we never clear this bit, it can be false-positive after
> uprobe_unregister() or uprobe_munmap() or if dup_mmap() hits the
> probed VM_DONTCOPY vma. But this is fine correctness-wise and has
> no effect unless the task hits the non-uprobe breakpoint.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

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