> On Jul 24, 2019, at 4:37 AM, Oleg Nesterov <[email protected]> wrote:
>
> On 07/24, Song Liu wrote:
>>
>> lock_page(old_page);
>> @@ -177,15 +180,24 @@ static int __replace_page(struct vm_area_struct *vma,
>> unsigned long addr,
>> mmu_notifier_invalidate_range_start(&range);
>> err = -EAGAIN;
>> if (!page_vma_mapped_walk(&pvmw)) {
>> - mem_cgroup_cancel_charge(new_page, memcg, false);
>> + if (!orig)
>> + mem_cgroup_cancel_charge(new_page, memcg, false);
>> goto unlock;
>> }
>> VM_BUG_ON_PAGE(addr != pvmw.address, old_page);
>>
>> get_page(new_page);
>> - page_add_new_anon_rmap(new_page, vma, addr, false);
>> - mem_cgroup_commit_charge(new_page, memcg, false, false);
>> - lru_cache_add_active_or_unevictable(new_page, vma);
>> + if (orig) {
>> + lock_page(new_page); /* for page_add_file_rmap() */
>> + page_add_file_rmap(new_page, false);
>
>
> Shouldn't we re-check new_page->mapping after lock_page() ? Or we can't
> race with truncate?
We can't race with truncate, because the file is open as binary and
protected with DENYWRITE (ETXTBSY).
>
>
> and I am worried this code can try to lock the same page twice...
> Say, the probed application does MADV_DONTNEED and then writes "int3"
> into vma->vm_file at the same address to fool verify_opcode().
>
Do you mean the case where old_page == new_page? I think this won't
happen, because in uprobe_write_opcode() we only do orig_page for
!is_register case.
Thanks,
Song
