linux-kernel - Re: [PATCH] lockdep: lock_set_subclass

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Message-ID: <Pine.LNX.4.64.0808012130510.11513@blonde.site>
Date:	Fri, 1 Aug 2008 21:33:47 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Miller <davem@...emloft.net>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] lockdep: lock_set_subclass - reset a held lock's subclass

On Fri, 1 Aug 2008, Jeremy Fitzhardinge wrote:
> Hugh Dickins wrote:
> > Please check the spin_lock_nested() in move_ptes() in mm/mremap.c.
> >
> > If you have down_write(&mm->mmap_sem) then you should be safe,
> > but may need to do something to placate lockdep.  If you don't
> > have down_write(&mm->mmap_sem), then I think you're in trouble?
> >
> > Not a big deal, the move_ptes() locking can be adjusted to suit
> > your rule, it was just easier to do it the way it is at the time.
> 
> Ah, yes, I did look at that.  I think it isn't an issue, because my code is
> called from dup_mmap(), activate_mm() or exit_mmap().
> 
> dup_mmap() already holds mmap_sem.
> 
> activate_mm() in exec doesn't hold the sem, but I don't think it's possible
> for anyone to be racing against it.
> activate_mm() in unshare doesn't seem to get used.
> 
> exit_mmap() gets called when there are no other users, so we'd better not be
> racing...

All safe against mremap, agreed.

Hugh
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