Re: [PATCH] parisc: mm: Fix a memory leak related to pmd not attached to the pgd

Mikulas Patocka
2015-07-13T12:48:54Z

On Mon, 13 Jul 2015, Christophe JAILLET wrote:

> Commit 0e0da48dee8d ("parisc: mm: don't count preallocated pmds")
> introduced a memory leak.
>
> After this commit, the 'return' statement in pmd_free is executed in all
> cases. Even for pmd that are not attached to the pgd.
> So 'free_pages' can never be called anymore, leading to a memory leak.
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

Acked-by: Mikulas Patocka <mpatocka@redhat.com>

also add this, so that it is backported to 4.0 and 4.2:
Cc: stable@vger.kernel.org # 4.0+
Fixes: 0e0da48dee8d

> ---
> This patch is *untested* as I don't have the hardware to test it.
>
> This is just a guess based on the indentation, the comment in the code
> and the commit log.
> ---
> arch/parisc/include/asm/pgalloc.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/parisc/include/asm/pgalloc.h b/arch/parisc/include/asm/pgalloc.h
> index 3a08eae..f66d3738 100644
> --- a/arch/parisc/include/asm/pgalloc.h
> +++ b/arch/parisc/include/asm/pgalloc.h
> @@ -72,7 +72,7 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
>
> static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd)
> {
> - if(pmd_flag(*pmd) & PxD_FLAG_ATTACHED)
> + if (pmd_flag(*pmd) & PxD_FLAG_ATTACHED) {
> /*
> * This is the permanent pmd attached to the pgd;
> * cannot free it.
> @@ -81,6 +81,7 @@ static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd)
> */
> mm_inc_nr_pmds(mm);
> return;
> + }
> free_pages((unsigned long)pmd, PMD_ORDER);
> }
>
> --
> 2.1.4
>