From: Jerome Glisse <jglisse@redhat.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v2 10/11] mm/hmm: add helpers for driver to safely take the mmap_sem v2
Date: Thu, 28 Mar 2019 19:24:04 -0400 [thread overview]
Message-ID: <20190328232404.GK13560@redhat.com> (raw)
In-Reply-To: <9e414b8c-0f98-a2f7-4f46-d335c015fc1b@nvidia.com>
On Thu, Mar 28, 2019 at 04:20:37PM -0700, John Hubbard wrote:
> On 3/28/19 4:05 PM, Jerome Glisse wrote:
> > On Thu, Mar 28, 2019 at 03:43:33PM -0700, John Hubbard wrote:
> >> On 3/28/19 3:40 PM, Jerome Glisse wrote:
> >>> On Thu, Mar 28, 2019 at 03:25:39PM -0700, John Hubbard wrote:
> >>>> On 3/28/19 3:08 PM, Jerome Glisse wrote:
> >>>>> On Thu, Mar 28, 2019 at 02:41:02PM -0700, John Hubbard wrote:
> >>>>>> On 3/28/19 2:30 PM, Jerome Glisse wrote:
> >>>>>>> On Thu, Mar 28, 2019 at 01:54:01PM -0700, John Hubbard wrote:
> >>>>>>>> On 3/25/19 7:40 AM, jglisse@redhat.com wrote:
> >>>>>>>>> From: Jérôme Glisse <jglisse@redhat.com>
> >>>> [...]
> >>>> OK, so let's either drop this patch, or if merge windows won't allow that,
> >>>> then *eventually* drop this patch. And instead, put in a hmm_sanity_check()
> >>>> that does the same checks.
> >>>
> >>> RDMA depends on this, so does the nouveau patchset that convert to new API.
> >>> So i do not see reason to drop this. They are user for this they are posted
> >>> and i hope i explained properly the benefit.
> >>>
> >>> It is a common pattern. Yes it only save couple lines of code but down the
> >>> road i will also help for people working on the mmap_sem patchset.
> >>>
> >>
> >> It *adds* a couple of lines that are misleading, because they look like they
> >> make things safer, but they don't actually do so.
> >
> > It is not about safety, sorry if it confused you but there is nothing about
> > safety here, i can add a big fat comment that explains that there is no safety
> > here. The intention is to allow the page fault handler that potential have
> > hundred of page fault queue up to abort as soon as it sees that it is pointless
> > to keep faulting on a dying process.
> >
> > Again if we race it is _fine_ nothing bad will happen, we are just doing use-
> > less work that gonna be thrown on the floor and we are just slowing down the
> > process tear down.
> >
>
> In addition to a comment, how about naming this thing to indicate the above
> intention? I have a really hard time with this odd down_read() wrapper, which
> allows code to proceed without really getting a lock. It's just too wrong-looking.
> If it were instead named:
>
> hmm_is_exiting()
What about: hmm_lock_mmap_if_alive() ?
>
> and had a comment about why racy is OK, then I'd be a lot happier. :)
Will add fat comment.
Cheers,
Jérôme
next prev parent reply other threads:[~2019-03-28 23:24 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-25 14:40 [PATCH v2 00/11] Improve HMM driver API v2 jglisse
2019-03-25 14:40 ` [PATCH v2 01/11] mm/hmm: select mmu notifier when selecting HMM jglisse
2019-03-28 20:33 ` John Hubbard
2019-03-29 21:15 ` Jerome Glisse
2019-03-29 21:42 ` John Hubbard
2019-03-25 14:40 ` [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2 jglisse
2019-03-28 11:07 ` Ira Weiny
2019-03-28 19:11 ` Jerome Glisse
2019-03-28 20:43 ` John Hubbard
2019-03-28 21:21 ` Jerome Glisse
2019-03-29 0:39 ` John Hubbard
2019-03-28 16:57 ` Ira Weiny
2019-03-29 1:00 ` Jerome Glisse
2019-03-29 1:18 ` John Hubbard
2019-03-29 1:50 ` Jerome Glisse
2019-03-28 18:21 ` Ira Weiny
2019-03-29 2:25 ` Jerome Glisse
2019-03-29 20:07 ` John Hubbard
2019-03-29 2:11 ` John Hubbard
2019-03-29 2:22 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 03/11] mm/hmm: do not erase snapshot when a range is invalidated jglisse
2019-03-25 14:40 ` [PATCH v2 04/11] mm/hmm: improve and rename hmm_vma_get_pfns() to hmm_range_snapshot() v2 jglisse
2019-03-28 13:30 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 05/11] mm/hmm: improve and rename hmm_vma_fault() to hmm_range_fault() v2 jglisse
2019-03-28 13:43 ` Ira Weiny
2019-03-28 22:03 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 06/11] mm/hmm: improve driver API to work and wait over a range v2 jglisse
2019-03-28 13:11 ` Ira Weiny
2019-03-28 21:39 ` Jerome Glisse
2019-03-28 16:12 ` Ira Weiny
2019-03-29 0:56 ` Jerome Glisse
2019-03-28 18:49 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 07/11] mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays jglisse
2019-03-28 21:59 ` John Hubbard
2019-03-28 22:12 ` Jerome Glisse
2019-03-28 22:19 ` John Hubbard
2019-03-28 22:31 ` Jerome Glisse
2019-03-28 22:40 ` John Hubbard
2019-03-28 23:21 ` Jerome Glisse
2019-03-28 23:28 ` John Hubbard
2019-03-28 16:42 ` Ira Weiny
2019-03-29 1:17 ` Jerome Glisse
2019-03-29 1:30 ` John Hubbard
2019-03-29 1:42 ` Jerome Glisse
2019-03-29 1:59 ` Jerome Glisse
2019-03-29 2:05 ` John Hubbard
2019-03-29 2:12 ` Jerome Glisse
2019-03-28 23:43 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 08/11] mm/hmm: mirror hugetlbfs (snapshoting, faulting and DMA mapping) v2 jglisse
2019-03-28 16:53 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 09/11] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem v2 jglisse
2019-03-28 18:04 ` Ira Weiny
2019-03-29 2:17 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 10/11] mm/hmm: add helpers for driver to safely take the mmap_sem v2 jglisse
2019-03-28 20:54 ` John Hubbard
2019-03-28 21:30 ` Jerome Glisse
2019-03-28 21:41 ` John Hubbard
2019-03-28 22:08 ` Jerome Glisse
2019-03-28 22:25 ` John Hubbard
2019-03-28 22:40 ` Jerome Glisse
2019-03-28 22:43 ` John Hubbard
2019-03-28 23:05 ` Jerome Glisse
2019-03-28 23:20 ` John Hubbard
2019-03-28 23:24 ` Jerome Glisse [this message]
2019-03-28 23:34 ` John Hubbard
2019-03-28 18:44 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 11/11] mm/hmm: add an helper function that fault pages and map them to a device v2 jglisse
2019-04-01 11:59 ` Souptick Joarder
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