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;
Regards,
Wanpeng Li
>Thanks.
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