Messages in this thread | | | Date | Fri, 16 Oct 2009 17:01:30 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH] mm: call pte_unmap() against a proper pte (Re: [PATCH 7/9] swap_info: swap count continuations) |
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On Fri, 16 Oct 2009 15:30:56 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> Hi. > > > @@ -645,6 +648,7 @@ static int copy_pte_range(struct mm_stru > > spinlock_t *src_ptl, *dst_ptl; > > int progress = 0; > > int rss[2]; > > + swp_entry_t entry = (swp_entry_t){0}; > > > > again: > > rss[1] = rss[0] = 0; > > @@ -671,7 +675,10 @@ again: > > progress++; > > continue; > > } > > - copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, vma, addr, rss); > > + entry.val = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, > > + vma, addr, rss); > > + if (entry.val) > > + break; > > progress += 8; > > } while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end); > > > It isn't the fault of only this patch, but I think breaking the loop without incrementing > dst_pte(and src_pte) would be bad behavior because we do unmap_pte(dst_pte - 1) later. > (current copy_pte_range() already does it though... and this is only problematic > when we break the first loop, IIUC.) >
oh, yes. nice catch!
> > @@ -681,6 +688,12 @@ again: > > add_mm_rss(dst_mm, rss[0], rss[1]); > > pte_unmap_unlock(dst_pte - 1, dst_ptl); > > cond_resched(); > > + > > + if (entry.val) { > > + if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) > > + return -ENOMEM; > > + progress = 0; > > + } > > if (addr != end) > > goto again; > > return 0; > > I've searched other places where we break a similar loop and do pte_unmap(pte - 1). > Current copy_pte_range() and apply_to_pte_range() has the same problem. >
> How about a patch like this ? > === > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > There are some places where we do like: > > pte = pte_map(); > do { > (do break in some conditions) > } while (pte++, ...); > pte_unmap(pte - 1); > > But if the loop breaks at the first loop, pte_unmap() unmaps invalid pte. > > This patch is a fix for this problem. > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
seems correct.
Reviewd-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> --- > mm/memory.c | 11 +++++++---- > 1 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 72a2494..492de38 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -641,6 +641,7 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *vma, > unsigned long addr, unsigned long end) > { > + pte_t *orig_src_pte, *orig_dst_pte; > pte_t *src_pte, *dst_pte; > spinlock_t *src_ptl, *dst_ptl; > int progress = 0; > @@ -654,6 +655,8 @@ again: > src_pte = pte_offset_map_nested(src_pmd, addr); > src_ptl = pte_lockptr(src_mm, src_pmd); > spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > + orig_src_pte = src_pte; > + orig_dst_pte = dst_pte; > arch_enter_lazy_mmu_mode(); > > do { > @@ -677,9 +680,9 @@ again: > > arch_leave_lazy_mmu_mode(); > spin_unlock(src_ptl); > - pte_unmap_nested(src_pte - 1); > + pte_unmap_nested(orig_src_pte); > add_mm_rss(dst_mm, rss[0], rss[1]); > - pte_unmap_unlock(dst_pte - 1, dst_ptl); > + pte_unmap_unlock(orig_dst_pte, dst_ptl); > cond_resched(); > if (addr != end) > goto again; > @@ -1822,10 +1825,10 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd, > token = pmd_pgtable(*pmd); > > do { > - err = fn(pte, token, addr, data); > + err = fn(pte++, token, addr, data); > if (err) > break; > - } while (pte++, addr += PAGE_SIZE, addr != end); > + } while (addr += PAGE_SIZE, addr != end); > > arch_leave_lazy_mmu_mode(); > >
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