linux-kernel - Re: [PATCH] drivers/virt/fsl_hypervisor: Correcting error handling path

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Date:   Fri, 22 May 2020 15:53:50 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, jgg@...pe.ca, dsterba@...e.com,
        arnd@...db.de, ira.weiny@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/virt/fsl_hypervisor: Correcting error handling
 path

On Thu, May 14, 2020 at 01:53:16AM +0530, Souptick Joarder wrote:
> First, when memory allocation for sg_list_unaligned failed, there
> is no point of calling put_pages() as we haven't pinned any pages.
> 
> Second, if get_user_pages_fast() failed we should unpinned num_pinned
> pages, no point of checking till num_pages.
> 
> This will address both.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>

If gup_flags were | FOLL_LONGTERM then this patch would fix a double
free because of the put_page() in __gup_longterm_locked().

mm/gup.c
  1786                  if (check_dax_vmas(vmas_tmp, rc)) {
  1787                          for (i = 0; i < rc; i++)
  1788                                  put_page(pages[i]);
                                        ^^^^^^^^^^^^^^^^^^^
put_page() here and also in the caller.

  1789                          rc = -EOPNOTSUPP;
  1790                          goto out;
  1791                  }

But since this isn't FOLL_LONGTERM the patch is a nice cleanup which
doesn't affect run time.

Reviewed-by: Dan Carpenter <dan.carpenter@...cle.com>

regards,
dan carpenter