linux-kernel - Re: [PATCH 4/5] mm/hmm: hmm_vma_fault() doesn't always call hmm_range

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Date:   Tue, 7 May 2019 18:45:54 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
        John Hubbard <jhubbard@...dia.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/5] mm/hmm: hmm_vma_fault() doesn't always call hmm_range_unregister()

On Tue, May 7, 2019 at 5:00 AM <rcampbell@...dia.com> wrote:
>
> From: Ralph Campbell <rcampbell@...dia.com>
>
> The helper function hmm_vma_fault() calls hmm_range_register() but is
> missing a call to hmm_range_unregister() in one of the error paths.
> This leads to a reference count leak and ultimately a memory leak on
> struct hmm.
>
> Always call hmm_range_unregister() if hmm_range_register() succeeded.

How about * Call hmm_range_unregister() in error path if
hmm_range_register() succeeded* ?

>
> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Souptick Joarder <jrdr.linux@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  include/linux/hmm.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 35a429621e1e..fa0671d67269 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -559,6 +559,7 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
>                 return (int)ret;
>
>         if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
> +               hmm_range_unregister(range);
>                 /*
>                  * The mmap_sem was taken by driver we release it here and
>                  * returns -EAGAIN which correspond to mmap_sem have been
> @@ -570,13 +571,13 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
>
>         ret = hmm_range_fault(range, block);
>         if (ret <= 0) {
> +               hmm_range_unregister(range);

what is the reason to moved it up ?

>                 if (ret == -EBUSY || !ret) {
>                         /* Same as above, drop mmap_sem to match old API. */
>                         up_read(&range->vma->vm_mm->mmap_sem);
>                         ret = -EBUSY;
>                 } else if (ret == -EAGAIN)
>                         ret = -EBUSY;
> -               hmm_range_unregister(range);
>                 return ret;
>         }
>         return 0;
> --
> 2.20.1
>