Re: [PATCH 4.4 022/118] IB/uverbs: Fix race between uverbs_close and remove_one

From	Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 4.4 022/118] IB/uverbs: Fix race between uverbs_close and remove_one
Date	2016-10-03 19:10 +0200
Message-ID	<soeUx-7Mb-13@gated-at.bofh.it> (permalink)
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On Mon, Oct 03, 2016 at 02:28:40PM +0200, Vegard Nossum wrote:

> This lock is literally called "cleanup mutex" and it's not really
> documented what data it protects. Is there a better solution here?

I agree it is very complex and hard to understand. This is why it
needed patching :| The mutex is in fact pretty much locking
code. (ensuring that ib_uverbs_cleanup_ucontext only runs on one
thread during this race)

There are at least three locks involved in this process. I didn't see
any obvious way to extend any of the other locks to handle this case.

The argument against most simple solutions (eg a rw lock rather than
the srcu) has been performance on these paths.

Jason

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Re: [PATCH 4.4 022/118] IB/uverbs: Fix race between uverbs_close and remove_one Vegard Nossum <vegard.nossum@gmail.com> - 2016-10-03 14:30 +0200
  Re: [PATCH 4.4 022/118] IB/uverbs: Fix race between uverbs_close and  remove_one Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-03 19:10 +0200

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