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Subject: Re: [PATCH 07/12] vhost-scsi: convert put_page() to put_user_page*()
To:     <john.hubbard@gmail.com>, Andrew Morton <akpm@linux-foundation.org>
CC:     Alexander Viro <viro@zeniv.linux.org.uk>,
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References: <20190724042518.14363-1-jhubbard@nvidia.com>
 <20190724042518.14363-8-jhubbard@nvidia.com>
From:   John Hubbard <jhubbard@nvidia.com>
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On 7/23/19 9:25 PM, john.hubbard@gmail.com wrote:
> From: J=C3=A9r=C3=B4me Glisse <jglisse@redhat.com>
>=20
> For pages that were retained via get_user_pages*(), release those pages
> via the new put_user_page*() routines, instead of via put_page().
>=20
> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
> ("mm: introduce put_user_page*(), placeholder versions").
>=20
> Changes from J=C3=A9r=C3=B4me's original patch:
>=20
> * Changed a WARN_ON to a BUG_ON.
>=20

Clearly, the above commit log has it backwards (this is quite my night
for typos).  Please read that as "changed a BUG_ON to a WARN_ON".

I'll correct the commit description in next iteration of this patchset.

...

> +	/*
> +	 * Here in all cases we should have an IOVEC which use GUP. If that is
> +	 * not the case then we will wrongly call put_user_page() and the page
> +	 * refcount will go wrong (this is in vhost_scsi_release_cmd())
> +	 */
> +	WARN_ON(!iov_iter_get_pages_use_gup(iter));
> +
...

thanks,
--=20
John Hubbard
NVIDIA