From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) (using TLSv1.2 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 20F391A00A2 for ; Sun, 14 Feb 2016 16:33:00 +1100 (AEDT) Received: from localhost by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 14 Feb 2016 00:32:57 -0500 Received: from b01cxnp23033.gho.pok.ibm.com (b01cxnp23033.gho.pok.ibm.com [9.57.198.28]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id CFE5E38C8026 for ; Sun, 14 Feb 2016 00:32:54 -0500 (EST) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by b01cxnp23033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u1E5WsdD28115160 for ; Sun, 14 Feb 2016 05:32:54 GMT Received: from d01av02.pok.ibm.com (localhost [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u1E5Wr1k008819 for ; Sun, 14 Feb 2016 00:32:54 -0500 From: "Aneesh Kumar K.V" To: Michael Ellerman , benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, Mel Gorman , "Kirill A. Shutemov" Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update In-Reply-To: <20160209121606.EA46C140B97@ozlabs.org> References: <20160209121606.EA46C140B97@ozlabs.org> Date: Sun, 14 Feb 2016 11:02:47 +0530 Message-ID: <877fi7ambk.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Michael Ellerman writes: > On Tue, 2016-09-02 at 01:20:31 UTC, "Aneesh Kumar K.V" wrote: >> With ppc64 we use the deposited pgtable_t to store the hash pte slot >> information. We should not withdraw the deposited pgtable_t without >> marking the pmd none. This ensure that low level hash fault handling >> will skip this huge pte and we will handle them at upper levels. >> >> Recent change to pmd splitting changed the above in order to handle the >> race between pmd split and exit_mmap. The race is explained below. >> >> Consider following race: >> >> CPU0 CPU1 >> shrink_page_list() >> add_to_swap() >> split_huge_page_to_list() >> __split_huge_pmd_locked() >> pmdp_huge_clear_flush_notify() >> // pmd_none() == true >> exit_mmap() >> unmap_vmas() >> zap_pmd_range() >> // no action on pmd since pmd_none() == true >> pmd_populate() >> >> As result the THP will not be freed. The leak is detected by check_mm(): >> >> BUG: Bad rss-counter state mm:ffff880058d2e580 idx:1 val:512 >> >> The above required us to not mark pmd none during a pmd split. >> >> The fix for ppc is to clear the huge pte of _PAGE_USER, so that low >> level fault handling code skip this pte. At higher level we do take ptl >> lock. That should serialze us against the pmd split. Once the lock is >> acquired we do check the pmd again using pmd_same. That should always >> return false for us and hence we should retry the access. We do the >> pmd_same check in all case after taking plt with >> THP (do_huge_pmd_wp_page, do_huge_pmd_numa_page and >> huge_pmd_set_accessed) >> >> Also make sure we wait for irq disable section in other cpus to finish >> before flipping a huge pte entry with a regular pmd entry. Code paths >> like find_linux_pte_or_hugepte depend on irq disable to get >> a stable pte_t pointer. A parallel thp split need to make sure we >> don't convert a pmd pte to a regular pmd entry without waiting for the >> irq disable section to finish. >> >> Acked-by: Kirill A. Shutemov >> Signed-off-by: Aneesh Kumar K.V > > Applied to powerpc fixes, thanks. > > https://git.kernel.org/powerpc/c/9db4cd6c21535a4846b38808f3 > Can we apply the below hunk ?. The reason for marking pmd none was to avoid clearing both _PAGE_USER and _PAGE_PRESENT on the pte. At pmd level that used to mean a hugepd pointer before. We did fix that earlier by introducing _PAGE_PTE. But then I was thinking it was harmless to mark pmd none. Now marking it one will still result in the race I explained above, eventhough the window is much smaller now. diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c index c8a00da39969..03f6e72697d0 100644 --- a/arch/powerpc/mm/pgtable_64.c +++ b/arch/powerpc/mm/pgtable_64.c @@ -694,7 +694,7 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr, void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp) { - pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0); + pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0); /* * This ensures that generic code that rely on IRQ disabling * to prevent a parallel THP split work as expected.