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Date: Fri, 22 Mar 2019 13:53:42 +0530 From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: "Kirill A . Shutemov" <kirill@...temov.name>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>, Andrea Arcangeli <aarcange@...hat.com> Subject: Re: [PATCH] mm: page_mkclean vs MADV_DONTNEED race Andrew Morton <akpm@...ux-foundation.org> writes: > On Thu, 21 Mar 2019 09:36:10 +0530 "Aneesh Kumar K.V" <aneesh.kumar@...ux.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@...ux.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@...ux.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
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