linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jerome Glisse <jglisse@redhat.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Felix.Kuehling@amd.com, linux-rdma@vger.kernel.org,
	linux-mm@kvack.org, Andrea Arcangeli <aarcange@redhat.com>,
	dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
	Ben Skeggs <bskeggs@redhat.com>,
	Philip Yang <Philip.Yang@amd.com>
Subject: Re: [PATCH v3 hmm 08/12] mm/hmm: Remove racy protection against double-unregistration
Date: Tue, 18 Jun 2019 10:13:24 -0300	[thread overview]
Message-ID: <20190618131324.GF6961@ziepe.ca> (raw)
In-Reply-To: <20190615141612.GH17724@infradead.org>

On Sat, Jun 15, 2019 at 07:16:12AM -0700, Christoph Hellwig wrote:
> On Thu, Jun 13, 2019 at 09:44:46PM -0300, Jason Gunthorpe wrote:
> > From: Jason Gunthorpe <jgg@mellanox.com>
> > 
> > No other register/unregister kernel API attempts to provide this kind of
> > protection as it is inherently racy, so just drop it.
> > 
> > Callers should provide their own protection, it appears nouveau already
> > does, but just in case drop a debugging POISON.
> 
> I don't even think we even need to bother with the POISON, normal list
> debugging will already catch a double unregistration anyway.

mirror->hmm isn't a list so list debugging won't help.

My concern when I wrote this was that one of the in flight patches I
can't see might be depending on this double-unregister-is-safe
behavior, so I wanted them to crash reliably.

It is a really overly conservative thing to do..

Thanks,
Jason


  reply	other threads:[~2019-06-18 13:13 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-14  0:44 [PATCH v3 hmm 00/12] mm/hmm: Various revisions from a locking/code review Jason Gunthorpe
2019-06-14  0:44 ` [PATCH v3 hmm 01/12] mm/hmm: fix use after free with struct hmm in the mmu notifiers Jason Gunthorpe
2019-06-15 13:56   ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 02/12] mm/hmm: Use hmm_mirror not mm as an argument for hmm_range_register Jason Gunthorpe
2019-06-15 13:59   ` Christoph Hellwig
2019-06-18 13:05     ` Jason Gunthorpe
2019-06-19  8:14       ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 03/12] mm/hmm: Hold a mmgrab from hmm to mm Jason Gunthorpe
2019-06-15 13:59   ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 04/12] mm/hmm: Simplify hmm_get_or_create and make it reliable Jason Gunthorpe
2019-06-15 14:12   ` Christoph Hellwig
2019-06-18  0:36     ` Jason Gunthorpe
2019-06-18 18:55     ` Jason Gunthorpe
2019-06-14  0:44 ` [PATCH v3 hmm 05/12] mm/hmm: Remove duplicate condition test before wait_event_timeout Jason Gunthorpe
2019-06-15 14:12   ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 06/12] mm/hmm: Hold on to the mmget for the lifetime of the range Jason Gunthorpe
2019-06-15 14:14   ` Christoph Hellwig
2019-06-18 15:11     ` Jason Gunthorpe
2019-06-19  8:18       ` Christoph Hellwig
2019-06-19 11:34         ` Jason Gunthorpe
2019-06-19 11:54           ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 07/12] mm/hmm: Use lockdep instead of comments Jason Gunthorpe
2019-06-15 14:14   ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 08/12] mm/hmm: Remove racy protection against double-unregistration Jason Gunthorpe
2019-06-15 14:16   ` Christoph Hellwig
2019-06-18 13:13     ` Jason Gunthorpe [this message]
2019-06-18 13:27       ` Christoph Hellwig
2019-06-18 18:57         ` Jason Gunthorpe
2019-06-19  8:19           ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 09/12] mm/hmm: Poison hmm_range during unregister Jason Gunthorpe
2019-06-15 14:17   ` Christoph Hellwig
2019-06-18 18:04     ` Jason Gunthorpe
2019-06-14  0:44 ` [PATCH v3 hmm 10/12] mm/hmm: Do not use list*_rcu() for hmm->ranges Jason Gunthorpe
2019-06-15 14:18   ` Christoph Hellwig
2019-06-18  0:38     ` Jason Gunthorpe
2019-06-14  0:44 ` [PATCH v3 hmm 11/12] mm/hmm: Remove confusing comment and logic from hmm_release Jason Gunthorpe
2019-06-15 14:21   ` Christoph Hellwig
2019-06-18  0:45     ` Jason Gunthorpe
2019-06-18  5:37       ` Christoph Hellwig
2019-06-19  0:53         ` Kuehling, Felix
2019-06-19  8:07           ` Christoph Hellwig
2019-06-19 11:56             ` Jason Gunthorpe
2019-06-19 12:03               ` Christoph Hellwig
2019-06-14  0:44 ` [PATCH v3 hmm 12/12] mm/hmm: Fix error flows in hmm_invalidate_range_start Jason Gunthorpe
2019-06-15 14:25   ` Christoph Hellwig

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190618131324.GF6961@ziepe.ca \
    --to=jgg@ziepe.ca \
    --cc=Felix.Kuehling@amd.com \
    --cc=Philip.Yang@amd.com \
    --cc=aarcange@redhat.com \
    --cc=amd-gfx@lists.freedesktop.org \
    --cc=bskeggs@redhat.com \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=hch@infradead.org \
    --cc=jglisse@redhat.com \
    --cc=jhubbard@nvidia.com \
    --cc=linux-mm@kvack.org \
    --cc=linux-rdma@vger.kernel.org \
    --cc=rcampbell@nvidia.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox