Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] mm: fix potential pte_unmap_unlock pte error
To:     <osalvador@suse.de>, Michal Hocko <mhocko@suse.com>
CC:     <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <linmiaohe@huawei.com>,
        <linfeilong@huawei.com>
References: <20201015121534.50910-1-luoshijie1@huawei.com>
 <20201016123137.GH22589@dhcp22.suse.cz>
 <f99d9457ae88f3692e57cce86d0e22e8@suse.de>
 <20201016131112.GJ22589@dhcp22.suse.cz>
 <20201016131531.GK22589@dhcp22.suse.cz>
 <20201016134215.GL22589@dhcp22.suse.cz>
 <8b1e52b7a07b9ff1be9badb73209abda@suse.de>
From:   Shijie Luo <luoshijie1@huawei.com>
Message-ID: <bc1ea882-9434-0009-0dc1-849954f80a3a@huawei.com>
Date:   Sat, 17 Oct 2020 09:55:42 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.6.1
MIME-Version: 1.0
In-Reply-To: <8b1e52b7a07b9ff1be9badb73209abda@suse.de>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk

On 2020/10/16 22:05, osalvador@suse.de wrote:
> On 2020-10-16 15:42, Michal Hocko wrote:
>> OK, I finally managed to convince my friday brain to think and grasped
>> what the code is intended to do. The loop is hairy and we want to
>> prevent from spurious EIO when all the pages are on a proper node. So
>> the check has to be done inside the loop. Anyway I would find the
>> following fix less error prone and easier to follow
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index eddbe4e56c73..8cc1fc9c4d13 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -525,7 +525,7 @@ static int queue_pages_pte_range(pmd_t *pmd,
>> unsigned long addr,
>>      unsigned long flags = qp->flags;
>>      int ret;
>>      bool has_unmovable = false;
>> -    pte_t *pte;
>> +    pte_t *pte, *mapped_pte;
>>      spinlock_t *ptl;
>>
>>      ptl = pmd_trans_huge_lock(pmd, vma);
>> @@ -539,7 +539,7 @@ static int queue_pages_pte_range(pmd_t *pmd,
>> unsigned long addr,
>>      if (pmd_trans_unstable(pmd))
>>          return 0;
>>
>> -    pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
>> +    mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
>>      for (; addr != end; pte++, addr += PAGE_SIZE) {
>>          if (!pte_present(*pte))
>>              continue;
>> @@ -571,7 +571,7 @@ static int queue_pages_pte_range(pmd_t *pmd,
>> unsigned long addr,
>>          } else
>>              break;
>>      }
>> -    pte_unmap_unlock(pte - 1, ptl);
>> +    pte_unmap_unlock(mapped_pte, ptl);
>>      cond_resched();
>>
>>      if (has_unmovable)
>
> It is more clear to grasp, definitely.
Yeah, this one is more comprehensible, I 'll send a v2 patch, thank you.