On Tue, Sep 03, 2013 at 03:51:39PM +0800, Wanpeng Li wrote:
> On Tue, Sep 03, 2013 at 04:42:21PM +0900, Joonsoo Kim wrote:
> >On Tue, Sep 03, 2013 at 03:01:46PM +0800, Wanpeng Li wrote:
> >> There is a race window between vmap_area free and show vmap_area information.
> >>
> >> A B
> >>
> >> remove_vm_area
> >> spin_lock(&vmap_area_lock);
> >> va->flags &= ~VM_VM_AREA;
> >> spin_unlock(&vmap_area_lock);
> >> spin_lock(&vmap_area_lock);
> >> if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEZING))
> >> return 0;
> >> if (!(va->flags & VM_VM_AREA)) {
> >> seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
> >> (void *)va->va_start, (void *)va->va_end,
> >> va->va_end - va->va_start);
> >> return 0;
> >> }
> >> free_unmap_vmap_area(va);
> >> flush_cache_vunmap
> >> free_unmap_vmap_area_noflush
> >> unmap_vmap_area
> >> free_vmap_area_noflush
> >> va->flags |= VM_LAZY_FREE
> >>
> >> The assumption is introduced by commit: d4033afd(mm, vmalloc: iterate vmap_area_list,
> >> instead of vmlist, in vmallocinfo()). This patch fix it by drop the assumption and
> >> keep not dump vm_map_ram allocation information as the logic before that commit.
> >>
> >> Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
> >> ---
> >> mm/vmalloc.c | 7 -------
> >> 1 file changed, 7 deletions(-)
> >>
> >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> >> index 5368b17..62b7932 100644
> >> --- a/mm/vmalloc.c
> >> +++ b/mm/vmalloc.c
> >> @@ -2586,13 +2586,6 @@ static int s_show(struct seq_file *m, void *p)
> >> if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEING))
> >> return 0;
> >>
> >> - if (!(va->flags & VM_VM_AREA)) {
> >> - seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
> >> - (void *)va->va_start, (void *)va->va_end,
> >> - va->va_end - va->va_start);
> >> - return 0;
> >> - }
> >> -
> >> v = va->vm;
> >>
> >> seq_printf(m, "0x%pK-0x%pK %7ld",
> >
> >Hello, Wanpeng.
> >
>
> Hi Joonsoo and Yanfei,
>
> >Did you test this patch?
> >
> >I guess that, With this patch, if there are some vm_map areas,
> >null pointer deference would occurs, since va->vm may be null for it.
> >
> >And with this patch, if this race really occur, null pointer deference
> >would occurs too, since va->vm is set to null in remove_vm_area().
> >
> >I think that this is not a right fix for this possible race.
> >
>
> How about append below to this patch?
>
> if (va->vm)
> v = va->vm;
> else
> return 0;
Hello,
I think that appending below code is better to represent it's purpose.
Maybe some comment is needed.
/* blablabla */
if (!(va->flags & VM_VM_AREA))
return 0;
And maybe we can remove below code snippet, since
either VM_LAZY_FREE or VM_LAZY_FREEING is not possible for !VM_VM_AREA case.
if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEING))
return 0;
Thanks.
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