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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id s6sm2681342otk.71.2021.06.07.17.06.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Jun 2021 17:06:47 -0700 (PDT) Date: Mon, 7 Jun 2021 17:06:28 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: "Aneesh Kumar K.V" Subject: Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout In-Reply-To: <20210607055131.156184-2-aneesh.kumar@linux.ibm.com> Message-ID: References: <20210607055131.156184-1-aneesh.kumar@linux.ibm.com> <20210607055131.156184-2-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linus Torvalds , npiggin@gmail.com, linux-mm@kvack.org, kaleshsingh@google.com, joel@joelfernandes.org, "Kirill A . Shutemov" , akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, 7 Jun 2021, Aneesh Kumar K.V wrote: > CPU 1 CPU 2 CPU 3 > > mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one > > mmap_write_lock_killable() > > addr = old_addr > lock(pte_ptl) > lock(pmd_ptl) > pmd = *old_pmd > pmd_clear(old_pmd) > flush_tlb_range(old_addr) > > *new_pmd = pmd > *new_addr = 10; and fills > TLB with new addr > and old pfn > > unlock(pmd_ptl) > ptep_clear_flush() > old pfn is free. > Stale TLB entry > > Fix this race by holding pmd lock in pageout. This still doesn't handle the race > between MOVE_PUD and pageout. > > Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions") > Link: https://lore.kernel.org/linux-mm/CAHk-=wgXVR04eBNtxQfevontWnP6FDm+oj5vauQXP3S-huwbPw@mail.gmail.com > Signed-off-by: Aneesh Kumar K.V This seems very wrong to me, to require another level of locking in the rmap lookup, just to fix some new pagetable games in mremap. But Linus asked "Am I missing something?": neither of you have mentioned mremap's take_rmap_locks(), so I hope that already meets your need. And if it needs to be called more often than before (see "need_rmap_locks"), that's probably okay. Hugh > --- > include/linux/rmap.h | 9 ++++++--- > mm/page_vma_mapped.c | 36 ++++++++++++++++++------------------ > 2 files changed, 24 insertions(+), 21 deletions(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index def5c62c93b3..272ab0c2b60b 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -207,7 +207,8 @@ struct page_vma_mapped_walk { > unsigned long address; > pmd_t *pmd; > pte_t *pte; > - spinlock_t *ptl; > + spinlock_t *pte_ptl; > + spinlock_t *pmd_ptl; > unsigned int flags; > }; > > @@ -216,8 +217,10 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw) > /* HugeTLB pte is set to the relevant page table entry without pte_mapped. */ > if (pvmw->pte && !PageHuge(pvmw->page)) > pte_unmap(pvmw->pte); > - if (pvmw->ptl) > - spin_unlock(pvmw->ptl); > + if (pvmw->pte_ptl) > + spin_unlock(pvmw->pte_ptl); > + if (pvmw->pmd_ptl) > + spin_unlock(pvmw->pmd_ptl); > } > > bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw); > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index 2cf01d933f13..87a2c94c7e27 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -47,8 +47,10 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) > return false; > } > } > - pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd); > - spin_lock(pvmw->ptl); > + if (USE_SPLIT_PTE_PTLOCKS) { > + pvmw->pte_ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd); > + spin_lock(pvmw->pte_ptl); > + } > return true; > } > > @@ -162,8 +164,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > if (!pvmw->pte) > return false; > > - pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte); > - spin_lock(pvmw->ptl); > + pvmw->pte_ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte); > + spin_lock(pvmw->pte_ptl); > if (!check_pte(pvmw)) > return not_found(pvmw); > return true; > @@ -179,6 +181,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > if (!pud_present(*pud)) > return false; > pvmw->pmd = pmd_offset(pud, pvmw->address); > + pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd); > /* > * Make sure the pmd value isn't cached in a register by the > * compiler and used as a stale value after we've observed a > @@ -186,7 +189,6 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > */ > pmde = READ_ONCE(*pvmw->pmd); > if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) { > - pvmw->ptl = pmd_lock(mm, pvmw->pmd); > if (likely(pmd_trans_huge(*pvmw->pmd))) { > if (pvmw->flags & PVMW_MIGRATION) > return not_found(pvmw); > @@ -206,14 +208,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > } > } > return not_found(pvmw); > - } else { > - /* THP pmd was split under us: handle on pte level */ > - spin_unlock(pvmw->ptl); > - pvmw->ptl = NULL; > } > - } else if (!pmd_present(pmde)) { > - return false; > - } > + } else if (!pmd_present(pmde)) > + return not_found(pvmw); > + > if (!map_pte(pvmw)) > goto next_pte; > while (1) { > @@ -233,19 +231,21 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > /* Did we cross page table boundary? */ > if (pvmw->address % PMD_SIZE == 0) { > pte_unmap(pvmw->pte); > - if (pvmw->ptl) { > - spin_unlock(pvmw->ptl); > - pvmw->ptl = NULL; > + if (pvmw->pte_ptl) { > + spin_unlock(pvmw->pte_ptl); > + pvmw->pte_ptl = NULL; > } > + spin_unlock(pvmw->pmd_ptl); > + pvmw->pmd_ptl = NULL; > goto restart; > } else { > pvmw->pte++; > } > } while (pte_none(*pvmw->pte)); > > - if (!pvmw->ptl) { > - pvmw->ptl = pte_lockptr(mm, pvmw->pmd); > - spin_lock(pvmw->ptl); > + if (USE_SPLIT_PTE_PTLOCKS && !pvmw->pte_ptl) { > + pvmw->pte_ptl = pte_lockptr(mm, pvmw->pmd); > + spin_lock(pvmw->pte_ptl); > } > } > } > -- > 2.31.1