linux-kernel - Re: [PATCH] mm/gup: protect unpin_user

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Date:   Sun, 20 Sep 2020 08:33:43 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>, alex.bou9@...il.com,
        gustavoars@...nel.org, Ira Weiny <ira.weiny@...el.com>,
        linux-kernel@...r.kernel.org, madhuparnabhowmik10@...il.com,
        mporter@...nel.crashing.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm/gup: protect unpin_user_pages() against npages==-ERRNO

On Thu, Sep 17, 2020 at 1:11 PM Dan Carpenter <dan.carpenter@...cle.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@...el.com>
> > Cc: Souptick Joarder <jrdr.linux@...il.com>
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > Signed-off-by: John Hubbard <jhubbard@...dia.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 ?