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Subject: Re: [PATCH v2 7/11] Uprobes Implementation
From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@elte.hu>,
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       Andrea Arcangeli <aarcange@redhat.com>
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Date: Wed, 12 May 2010 13:12:31 +0200
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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?