On 10/15/2013 06:34 PM, Hugh Dickins wrote:
> Revert 1ecfd533f4c5 ("mm/mremap.c: call pud_free() after fail calling
> pmd_alloc()"). The original code was correct: pud_alloc(), pmd_alloc(),
> pte_alloc_map() ensure that the pud, pmd, pt is already allocated, and
> seldom do they need to allocate; on failure, upper levels are freed if
> appropriate by the subsequent do_munmap(). Whereas 1ecfd533f4c5 did an
> unconditional pud_free() of a most-likely still-in-use pud: saved only
> by the near-impossiblity of pmd_alloc() failing.
>
What you said above sounds reasonable to me, but better to provide the
information below:
- pud_free() for pgd_alloc() in "arch/arm/mm/pgd.c".
- pud_free() for init_stub_pte() in "arch/um/kernel/skas/mmu.c".
- more details about do_munmap(), (e.g. do it need mm->page_table_lock)
or more details about the demo "most-likely still-in-use pud ...".
Hmm... I am not quite sure about the 3 things, and I will/should
continue analysing/learning about them, but better to get your reply. :-)
Thanks.
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
>
> mm/mremap.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> --- 3.12-rc5/mm/mremap.c 2013-09-16 17:37:56.841072270 -0700
> +++ linux/mm/mremap.c 2013-10-15 03:07:09.140091599 -0700
> @@ -25,7 +25,6 @@
> #include <asm/uaccess.h>
> #include <asm/cacheflush.h>
> #include <asm/tlbflush.h>
> -#include <asm/pgalloc.h>
>
> #include "internal.h"
>
> @@ -63,10 +62,8 @@ static pmd_t *alloc_new_pmd(struct mm_st
> return NULL;
>
> pmd = pmd_alloc(mm, pud, addr);
> - if (!pmd) {
> - pud_free(mm, pud);
> + if (!pmd)
> return NULL;
> - }
>
> VM_BUG_ON(pmd_trans_huge(*pmd));
>
>
>
--
Chen Gang
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