From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Dan Williams <dan.j.williams@intel.com>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH] mm: page_mkclean vs MADV_DONTNEED race
Date: Fri, 22 Mar 2019 13:53:42 +0530 [thread overview]
Message-ID: <8736nf8ghd.fsf@linux.ibm.com> (raw)
In-Reply-To: <20190321163147.cc2ff090a7388cdb7030eed0@linux-foundation.org>
Andrew Morton <akpm@linux-foundation.org> writes:
> On Thu, 21 Mar 2019 09:36:10 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote:
>
>> MADV_DONTNEED is handled with mmap_sem taken in read mode.
>> We call page_mkclean without holding mmap_sem.
>>
>> MADV_DONTNEED implies that pages in the region are unmapped and subsequent
>> access to the pages in that range is handled as a new page fault.
>> This implies that if we don't have parallel access to the region when
>> MADV_DONTNEED is run we expect those range to be unallocated.
>>
>> w.r.t page_mkclean we need to make sure that we don't break the MADV_DONTNEED
>> semantics. MADV_DONTNEED check for pmd_none without holding pmd_lock.
>> This implies we skip the pmd if we temporarily mark pmd none. Avoid doing
>> that while marking the page clean.
>>
>> Keep the sequence same for dax too even though we don't support MADV_DONTNEED
>> for dax mapping
>
> What were the runtime effects of the bug?
The bug was noticed by code review and I didn't observe any failures
w.r.t test run. This is similar to
commit 58ceeb6bec86d9140f9d91d71a710e963523d063
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date: Thu Apr 13 14:56:26 2017 -0700
thp: fix MADV_DONTNEED vs. MADV_FREE race
commit ced108037c2aa542b3ed8b7afd1576064ad1362a
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date: Thu Apr 13 14:56:20 2017 -0700
thp: fix MADV_DONTNEED vs. numa balancing race
>
> Did you consider a -stable backport?
Considering nobody reported issues w.r.t MADV_DONTNEED I was not sure.
-aneesh
prev parent reply other threads:[~2019-03-22 8:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-21 4:06 [PATCH] mm: page_mkclean vs MADV_DONTNEED race Aneesh Kumar K.V
2019-03-21 23:31 ` Andrew Morton
2019-03-22 8:23 ` Aneesh Kumar K.V [this message]
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