Re: [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap_sem in munmap

[Yang Shi <yang.shi@linux.alibaba.com>]

On 8/22/18 4:11 AM, Vlastimil Babka wrote:
> On 08/15/2018 08:49 PM, Yang Shi wrote:
>
>> +	start_vma = munmap_lookup_vma(mm, start, end);
>> +	if (!start_vma)
>> +		goto out;
>> +	if (IS_ERR(start_vma)) {
>> +		ret = PTR_ERR(start_vma);
>> +		goto out;
>> +	}
>> +
>> +	prev = start_vma->vm_prev;
>> +
>> +	if (unlikely(uf)) {
>> +		ret = userfaultfd_unmap_prep(start_vma, start, end, uf);
>> +		if (ret)
>> +			goto out;
>> +	}
>> +
> You sure it's ok to redo this in case of goto regular path? The
> preparations have some side-effects... I would rather move this after
> the regular path check?

This preparation sets vma->vm_userfaultfd_ctx.ctx for each vmas. But, 
before doing this, it calls has_unmap_ctx() to check if the ctx has been 
set or not. If it has been set, it just skip the vma. It sounds ok, right?