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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YyxzYTlyGhbb2MOu@infradead.org>
Date:   Thu, 22 Sep 2022 07:38:25 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
        John Hubbard <jhubbard@...dia.com>,
        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 Thu, Sep 22, 2022 at 03:22:48AM +0100, Al Viro wrote:
> What I'd like to have is the understanding of the places where we drop
> the references acquired by iov_iter_get_pages().  How do we decide
> whether to unpin?

Add a iov_iter_unpin_pages that does the right thing based on the
type.  (block will need a modified copy of it as it doesn't keep
the pages array around, but logic will be the same).

> E.g. pipe_buffer carries a reference to page and no
> way to tell whether it's a pinned one; results of iov_iter_get_pages()
> on ITER_IOVEC *can* end up there, but thankfully only from data-source
> (== WRITE, aka.  ITER_SOURCE) iov_iter.  So for those we don't care.
> Then there's nfs_request; AFAICS, we do need to pin the references in
> those if they are coming from nfs_direct_read_schedule_iovec(), but
> not if they come from readpage_async_filler().  How do we deal with
> coalescence, etc.?  It's been a long time since I really looked at
> that code...  Christoph, could you give any comments on that one?

I think the above should work, but I'll need to look at the NFS code
in more detail to be sure.