Messages in this thread |  | | Date | Tue, 15 Oct 2013 19:46:29 +0800 | From | Chen Gang <> | Subject | Re: [PATCH] mm: revert mremap pud_free anti-fix |
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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@google.com> > --- > > 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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