From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e37.co.us.ibm.com (e37.co.us.ibm.com [32.97.110.158]) (using TLSv1 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 036061A0190 for ; Tue, 9 Feb 2016 01:04:54 +1100 (AEDT) Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 8 Feb 2016 07:04:52 -0700 Received: from b03cxnp08026.gho.boulder.ibm.com (b03cxnp08026.gho.boulder.ibm.com [9.17.130.18]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id E2DAF3E40048 for ; Mon, 8 Feb 2016 07:04:49 -0700 (MST) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by b03cxnp08026.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u18E4nbE27131938 for ; Mon, 8 Feb 2016 07:04:49 -0700 Received: from d03av01.boulder.ibm.com (localhost [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u18E4mIw003323 for ; Mon, 8 Feb 2016 07:04:49 -0700 From: "Aneesh Kumar K.V" To: "Kirill A. Shutemov" Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, akpm@linux-foundation.org, Mel Gorman , "Kirill A. Shutemov" , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] powerpc/mm: Fix Multi hit ERAT cause by recent THP update In-Reply-To: <20160208075247.GB9075@node.shutemov.name> References: <1454912062-9681-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20160208075247.GB9075@node.shutemov.name> Date: Mon, 08 Feb 2016 19:34:32 +0530 Message-ID: <871t8n1eof.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: , "Kirill A. Shutemov" writes: > On Mon, Feb 08, 2016 at 11:44:22AM +0530, 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. > > I guess it worth mention that this serialization against ptl happens in > huge_pmd_set_accessed(), if I didn't miss anything. Ok will update the commit message with the below "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. >> >> Signed-off-by: Aneesh Kumar K.V ..... ... >> #ifndef __HAVE_ARCH_PTE_SAME >> static inline int pte_same(pte_t pte_a, pte_t pte_b) >> { >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 36c070167b71..b52d16a86e91 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -2860,6 +2860,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, >> young = pmd_young(*pmd); >> dirty = pmd_dirty(*pmd); >> >> + pmdp_huge_splitting_flush(vma, haddr, pmd); > > Let's call it pmdp_huge_split_prepare(). > > "_flush" part is ppc-specific implementation detail and generic code > should not expect tlb to be flushed there. Ok done > > Otherwise, > > Acked-by: Kirill A. Shutemov > >> pgtable = pgtable_trans_huge_withdraw(mm, pmd); >> pmd_populate(mm, &_pmd, pgtable); >> >> -- >> 2.5.0 >> -aneesh