linux-kernel - Re: [PATCH 5/6] NFS: direct-io: convert to FOLL

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Message-ID: <353f18ac-0792-2cb7-6675-868d0bd41d3d@nvidia.com>
Date:   Sat, 27 Aug 2022 16:55:18 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Miklos Szeredi <miklos@...redi.hu>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, Jan Kara <jack@...e.cz>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] NFS: direct-io: convert to FOLL_PIN pages

On 8/27/22 15:48, Al Viro wrote:
> On Sat, Aug 27, 2022 at 01:36:06AM -0700, John Hubbard wrote:
>> Convert the NFS Direct IO layer to use pin_user_pages_fast() and
>> unpin_user_page(), instead of get_user_pages_fast() and put_page().
> 
> Again, this stuff can be hit with ITER_BVEC iterators
> 
>> -		result = iov_iter_get_pages_alloc2(iter, &pagevec,
>> +		result = dio_w_iov_iter_pin_pages_alloc(iter, &pagevec,
>>  						  rsize, &pgbase);
> 
> and this will break on those.

If anyone has an example handy, of a user space program that leads
to this situation (O_DIRECT with ITER_BVEC), it would really help
me reach enlightenment a lot quicker in this area. :)

thanks,

-- 
John Hubbard
NVIDIA