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

From: Yang Shi <yang.shi@linux.alibaba.com>
To: Vlastimil Babka <vbabka@suse.cz>,
	mhocko@kernel.org, willy@infradead.org,
	ldufour@linux.vnet.ibm.com, kirill@shutemov.name,
	akpm@linux-foundation.org, peterz@infradead.org,
	mingo@redhat.com, acme@kernel.org,
	alexander.shishkin@linux.intel.com, jolsa@redhat.com,
	namhyung@kernel.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC v8 PATCH 3/5] mm: mmap: zap pages with read mmap_sem in munmap
Date: Wed, 22 Aug 2018 12:20:37 -0700	[thread overview]
Message-ID: <2f447d4e-9e16-8030-85f0-4e258a7eafa3@linux.alibaba.com> (raw)
In-Reply-To: <7145895b-ef56-f5ee-d139-609819d9a107@suse.cz>

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?