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From:   Christoph Hellwig <hch@lst.de>
To:     John Hubbard <jhubbard@nvidia.com>
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        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH 1/3] mm/gup: introduce __put_user_pages()
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References: <20190722223415.13269-1-jhubbard@nvidia.com> <20190722223415.13269-2-jhubbard@nvidia.com> <20190723055359.GC17148@lst.de> <8ab4899c-ec12-a713-cac2-d951fff2a347@nvidia.com>
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On Mon, Jul 22, 2019 at 11:33:32PM -0700, John Hubbard wrote:
> I'm seeing about 18 places where set_page_dirty() is used, in the call site
> conversions so far, and about 20 places where set_page_dirty_lock() is
> used. So without knowing how many of the former (if any) represent bugs,
> you can see why the proposal here supports both DIRTY and DIRTY_LOCK.

Well, it should be fairly easy to audit.  set_page_dirty() is only
safe if we are dealing with a file backed page where we have reference
on the inode it hangs off.  Which should basically be never or almost
never.

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 1/3] mm/gup: introduce __put_user_pages()
Date: Tue, 23 Jul 2019 17:36:40 +0200
Message-ID: <20190723153640.GB720@lst.de>
References: <20190722223415.13269-1-jhubbard@nvidia.com> <20190722223415.13269-2-jhubbard@nvidia.com> <20190723055359.GC17148@lst.de> <8ab4899c-ec12-a713-cac2-d951fff2a347@nvidia.com>
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List-Id: dri-devel@lists.freedesktop.org

On Mon, Jul 22, 2019 at 11:33:32PM -0700, John Hubbard wrote:
> I'm seeing about 18 places where set_page_dirty() is used, in the call site
> conversions so far, and about 20 places where set_page_dirty_lock() is
> used. So without knowing how many of the former (if any) represent bugs,
> you can see why the proposal here supports both DIRTY and DIRTY_LOCK.

Well, it should be fairly easy to audit.  set_page_dirty() is only
safe if we are dealing with a file backed page where we have reference
on the inode it hangs off.  Which should basically be never or almost
never.