linux-kernel - Re: [PATCH v2 7/11] Uprobes Implementation

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Date:	Wed, 12 May 2010 13:12:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>, Mel Gorman <mel@....ul.ie>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v2 7/11] Uprobes Implementation

On Wed, 2010-05-12 at 16:11 +0530, Srikar Dronamraju wrote:
> > We can't hold mmap_sem (for either read or write -- read would be
> > sufficient to serialize against mmap/mremap/munmap) from atomic uprobe
> > context, what we can do is validate that there is a INT3 on that
> > particular address, a mremap/munmap/munmap+mmap will either end not
> > having a pte entry for the address, or not have the INT3.
> 
> Did you mean "We can hold mmap_sem?" Else I am not sure if we can
> traverse the vma. Infact alloc_page_vma() needs mmap_sem to be acquired.
> Please clarify? 

OK, so maybe I misunderstood, this is from the INT3 trap handler, right?

We can _not_ take a sleeping lock from trap context. Why would you want
the vma anyway?

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