netdev - Re: [PATCH 07/12] vhost-scsi: convert put_page() to put_user

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Date:   Tue, 23 Jul 2019 21:34:56 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     <john.hubbard@...il.com>, Andrew Morton <akpm@...ux-foundation.org>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "David S . Miller" <davem@...emloft.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Latchesar Ionkov <lucho@...kov.net>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        <ceph-devel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <linux-block@...r.kernel.org>, <linux-cifs@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-nfs@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, <netdev@...r.kernel.org>,
        <samba-technical@...ts.samba.org>,
        <v9fs-developer@...ts.sourceforge.net>,
        <virtualization@...ts.linux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Ming Lei <ming.lei@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Boaz Harrosh <boaz@...xistor.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH 07/12] vhost-scsi: convert put_page() to put_user_page*()

On 7/23/19 9:25 PM, john.hubbard@...il.com wrote:
> From: Jérôme Glisse <jglisse@...hat.com>
> 
> For pages that were retained via get_user_pages*(), release those pages
> via the new put_user_page*() routines, instead of via put_page().
> 
> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
> ("mm: introduce put_user_page*(), placeholder versions").
> 
> Changes from Jérôme's original patch:
> 
> * Changed a WARN_ON to a BUG_ON.
> 

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,
-- 
John Hubbard
NVIDIA