On Tue, Sep 03, 2013 at 05:59:59PM +0900, Joonsoo Kim wrote:
>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;
>
Looks reasonable to me. ;-)
>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;
>
Agreed.
I will fold these in my patch and add your suggested-by. Thanks.
Regards,
Wanpeng Li
>Thanks.
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