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From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: "Thomas Hellström (Intel)" <thomas_os@shipmail.org>
Cc: "DRI Development" <dri-devel@lists.freedesktop.org>,
	"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Christian König" <christian.koenig@amd.com>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>,
	"moderated list:DMA BUFFER SHARING FRAMEWORK"
	<linaro-mm-sig@lists.linaro.org>,
	"Dave Chinner" <david@fromorbit.com>, "Qian Cai" <cai@lca.pw>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Jason Gunthorpe" <jgg@mellanox.com>,
	"Linux MM" <linux-mm@kvack.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>
Subject: Re: [PATCH] dma-resv: lockdep-prime address_space->i_mmap_rwsem for dma-resv
Date: Thu, 30 Jul 2020 15:17:14 +0200
Message-ID: <CAKMK7uFe-70DE5qOBJ6FwD8d_A0yZt+h5bCqA=e9QtYE1qwASQ@mail.gmail.com> (raw)
In-Reply-To: <38cbc4fb-3a88-47c4-2d6c-4d90f9be42e7@shipmail.org>

On Thu, Jul 30, 2020 at 2:17 PM Thomas Hellström (Intel)
<thomas_os@shipmail.org> wrote:
>
>
> On 7/28/20 3:58 PM, Daniel Vetter wrote:
> > GPU drivers need this in their shrinkers, to be able to throw out
> > mmap'ed buffers. Note that we also need dma_resv_lock in shrinkers,
> > but that loop is resolved by trylocking in shrinkers.
> >
> > So full hierarchy is now (ignore some of the other branches we already
> > have primed):
> >
> > mmap_read_lock -> dma_resv -> shrinkers -> i_mmap_lock_write
> >
> > I hope that's not inconsistent with anything mm or fs does, adding
> > relevant people.
> >
> Looks OK to me. The mapping_dirty_helpers run under the i_mmap_lock, but
> don't allocate any memory AFAICT.
>
> Since huge page-table-entry splitting may happen under the i_mmap_lock
> from unmap_mapping_range() it might be worth figuring out how new page
> directory pages are allocated, though.

ofc I'm not an mm expert at all, but I did try to scroll through all
i_mmap_lock_write/read callers. Found the following:

- kernel/events/uprobes.c in build_map_info:

            /*
             * Needs GFP_NOWAIT to avoid i_mmap_rwsem recursion through
             * reclaim. This is optimistic, no harm done if it fails.
             */

- I got lost in the hugetlb.c code and couldn't convince myself it's
not allocating page directories at various levels with something else
than GFP_KERNEL.

So looks like the recursion is clearly there and known, but the
hugepage code is too complex and flying over my head.
-Daniel

>
> /Thomas
>
>
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28 13:58 Daniel Vetter
2020-07-30 12:03 ` [Linaro-mm-sig] " Christian König
2020-07-30 12:17 ` Thomas Hellström (Intel)
2020-07-30 13:17   ` Daniel Vetter [this message]
2020-07-30 16:45     ` Thomas Hellström (Intel)
2020-09-17 13:19       ` Daniel Vetter

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