Re: [RFC 2/4] Deactivate mmap_sem assert

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC 2/4] Deactivate mmap_sem assert
Date	2017-04-19 16:00 +0200
Message-ID	<txYjf-46P-13@gated-at.bofh.it> (permalink)
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On Wed, Apr 19, 2017 at 03:45:50PM +0200, Laurent Dufour wrote:
> On 19/04/2017 14:30, Peter Zijlstra wrote:
> > On Wed, Apr 19, 2017 at 02:18:25PM +0200, Laurent Dufour wrote:
> >> When mmap_sem will be moved to a range lock, some assertion done in
> >> the code are no more valid, like the one ensuring mmap_sem is held.
> >>
> > 
> > Why are they no longer valid?
> 
> I didn't explain that very well..
> 
> When using a range lock we can't check that the lock is simply held, but
> if the range we are interesting on is locked or not.

I don't think it matters.. That is, in general you cannot assume
anything about the ranges, therefore, for deadlock analysis you have to
assume each range is the full range.

Once you're there, and assume that each range is the full range, this
test is once again trivial.

The fact that not all ranges are the full range, is merely a performance
consideration, but should not be a correctness issue.

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[RFC 2/4] Deactivate mmap_sem assert Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-19 14:20 +0200
  Re: [RFC 2/4] Deactivate mmap_sem assert Peter Zijlstra <peterz@infradead.org> - 2017-04-19 14:40 +0200
    Re: [RFC 2/4] Deactivate mmap_sem assert Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-19 15:50 +0200
      Re: [RFC 2/4] Deactivate mmap_sem assert Peter Zijlstra <peterz@infradead.org> - 2017-04-19 16:00 +0200

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