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From:   Souptick Joarder <jrdr.linux@gmail.com>
Date:   Sun, 20 Sep 2020 08:33:43 +0530
Message-ID: <CAFqt6zYFjGTJ=KUjHd5jf-ri5tCmo4HOLP1j3nsELFgcoEoLHQ@mail.gmail.com>
Subject: Re: [PATCH] mm/gup: protect unpin_user_pages() against npages==-ERRNO
To:     Dan Carpenter <dan.carpenter@oracle.com>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>, alex.bou9@gmail.com,
        gustavoars@kernel.org, Ira Weiny <ira.weiny@intel.com>,
        linux-kernel@vger.kernel.org, madhuparnabhowmik10@gmail.com,
        mporter@kernel.crashing.org, Matthew Wilcox <willy@infradead.org>
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On Thu, Sep 17, 2020 at 1:11 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Wed, Sep 16, 2020 at 11:57:06PM -0700, John Hubbard wrote:
> > As suggested by Dan Carpenter, fortify unpin_user_pages() just a bit,
> > against a typical caller mistake: check if the npages arg is really a
> > -ERRNO value, which would blow up the unpinning loop: WARN and return.
> >
> > If this new WARN_ON() fires, then the system *might* be leaking pages
> > (by leaving them pinned), but probably not. More likely, gup/pup
> > returned a hard -ERRNO error to the caller, who erroneously passed it
> > here.
> >
> > Cc: Ira Weiny <ira.weiny@intel.com>
> > Cc: Souptick Joarder <jrdr.linux@gmail.com>
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> > ---
> >
> > Hi Dan,
> >
> > Is is OK to use your signed-off-by here? Since you came up with this.
> >
>
> Yeah.  That's fine.

Do we need a similar check inside unpin_user_pages_dirty_lock(),
when make_dirty set to false ?