linux-kernel - Re: [PATCH v2 4/7] iov_iter: new iov_iter_pin

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Message-ID: <c46b63f6-d222-36cb-ffb4-558df20edf24@nvidia.com>
Date:   Thu, 22 Sep 2022 21:34:26 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Miklos Szeredi <miklos@...redi.hu>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        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 v2 4/7] iov_iter: new iov_iter_pin_pages*() routines

On 9/22/22 04:29, Jan Kara wrote:
> I don't think this will work. The pin nfs_direct_read_schedule_iovec()
> obtains needs to be released once the IO is completed. Not once the IO is
> submitted. Notice how nfs_create_request()->__nfs_create_request() gets
> another page reference which is released on completion
> (nfs_direct_read_completion->nfs_release_request->nfs_page_group_destroy->
> nfs_free_request->nfs_clear_request). And we need to stop releasing the
> obtained pin in nfs_direct_read_schedule_iovec() (and acquiring another
> reference in __nfs_create_request()) and instead propagate it to
> nfs_clear_request() where it can get released.
> 
> 								Honza

OK, now I see how that is supposed to work, thanks for explaining!


thanks,

-- 
John Hubbard
NVIDIA