Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934441AbdCVNON (ORCPT ); Wed, 22 Mar 2017 09:14:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:52157 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934248AbdCVNOA (ORCPT ); Wed, 22 Mar 2017 09:14:00 -0400 Date: Wed, 22 Mar 2017 08:29:09 -0400 From: Michal Hocko To: Naoya Horiguchi Cc: linux-mm@kvack.org, Andrew Morton , Hugh Dickins , "Kirill A. Shutemov" , Hillf Danton , linux-kernel@vger.kernel.org, Naoya Horiguchi , Mike Kravetz Subject: Re: [PATCH v1] mm, hugetlb: use pte_present() instead of pmd_present() in follow_huge_pmd() Message-ID: <20170322122909.GA1407@dhcp22.suse.cz> References: <1490149898-20231-1-git-send-email-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1490149898-20231-1-git-send-email-n-horiguchi@ah.jp.nec.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5148 Lines: 97 [CC Mike] On Wed 22-03-17 11:31:38, Naoya Horiguchi wrote: > I found the race condition which triggers the following bug when > move_pages() and soft offline are called on a single hugetlb page > concurrently. > > [61163.578957] Soft offlining page 0x119400 at 0x700000000000 > [61163.580062] BUG: unable to handle kernel paging request at ffffea0011943820 > [61163.580791] IP: follow_huge_pmd+0x143/0x190 > [61163.581203] PGD 7ffd2067 > [61163.581204] PUD 7ffd1067 > [61163.581471] PMD 0 > [61163.581723] > [61163.582052] Oops: 0000 [#1] SMP > [61163.582349] Modules linked in: binfmt_misc ppdev virtio_balloon parport_pc pcspkr i2c_piix4 parport i2c_core acpi_cpufreq ip_tables xfs libcrc32c ata_generic pata_acpi virtio_blk 8139too crc32c_intel ata_piix serio_raw libata virtio_pci 8139cp virtio_ring virtio mii floppy dm_mirror dm_region_hash dm_log dm_mod [last unloaded: cap_check] > [61163.585130] CPU: 0 PID: 22573 Comm: iterate_numa_mo Tainted: P OE 4.11.0-rc2-mm1+ #2 > [61163.586055] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011 > [61163.586627] task: ffff88007c951680 task.stack: ffffc90004bd8000 > [61163.587181] RIP: 0010:follow_huge_pmd+0x143/0x190 > [61163.587622] RSP: 0018:ffffc90004bdbcd0 EFLAGS: 00010202 > [61163.588096] RAX: 0000000465003e80 RBX: ffffea0004e34d30 RCX: 00003ffffffff000 > [61163.588818] RDX: 0000000011943800 RSI: 0000000000080001 RDI: 0000000465003e80 > [61163.589486] RBP: ffffc90004bdbd18 R08: 0000000000000000 R09: ffff880138d34000 > [61163.590097] R10: ffffea0004650000 R11: 0000000000c363b0 R12: ffffea0011943800 > [61163.590751] R13: ffff8801b8d34000 R14: ffffea0000000000 R15: 000077ff80000000 > [61163.591375] FS: 00007fc977710740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 > [61163.592068] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [61163.592627] CR2: ffffea0011943820 CR3: 000000007a746000 CR4: 00000000001406f0 > [61163.593330] Call Trace: > [61163.593556] follow_page_mask+0x270/0x550 > [61163.593908] SYSC_move_pages+0x4ea/0x8f0 > [61163.594253] ? lru_cache_add_active_or_unevictable+0x4b/0xd0 > [61163.594798] SyS_move_pages+0xe/0x10 > [61163.595113] do_syscall_64+0x67/0x180 > [61163.595434] entry_SYSCALL64_slow_path+0x25/0x25 > [61163.595837] RIP: 0033:0x7fc976e03949 > [61163.596148] RSP: 002b:00007ffe72221d88 EFLAGS: 00000246 ORIG_RAX: 0000000000000117 > [61163.596940] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc976e03949 > [61163.597567] RDX: 0000000000c22390 RSI: 0000000000001400 RDI: 0000000000005827 > [61163.598177] RBP: 00007ffe72221e00 R08: 0000000000c2c3a0 R09: 0000000000000004 > [61163.598842] R10: 0000000000c363b0 R11: 0000000000000246 R12: 0000000000400650 > [61163.599456] R13: 00007ffe72221ee0 R14: 0000000000000000 R15: 0000000000000000 > [61163.600067] Code: 81 e4 ff ff 1f 00 48 21 c2 49 c1 ec 0c 48 c1 ea 0c 4c 01 e2 49 bc 00 00 00 00 00 ea ff ff 48 c1 e2 06 49 01 d4 f6 45 bc 04 74 90 <49> 8b 7c 24 20 40 f6 c7 01 75 2b 4c 89 e7 8b 47 1c 85 c0 7e 2a > [61163.601845] RIP: follow_huge_pmd+0x143/0x190 RSP: ffffc90004bdbcd0 > [61163.602376] CR2: ffffea0011943820 > [61163.602767] ---[ end trace e4f81353a2d23232 ]--- > [61163.603236] Kernel panic - not syncing: Fatal exception > [61163.603706] Kernel Offset: disabled > > This bug is triggered when pmd_present() returns true for non-present > hugetlb, so fixing the present check in follow_huge_pmd() prevents it. > Using pmd_present() to determine present/non-present for hugetlb is > not correct, because pmd_present() checks multiple bits (not only > _PAGE_PRESENT) for historical reason and it can misjudge hugetlb state. > > Fixes: e66f17ff7177 ("mm/hugetlb: take page table lock in follow_huge_pmd()") > Signed-off-by: Naoya Horiguchi > Cc: [4.0+] > --- > mm/hugetlb.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git v4.11-rc2-mmotm-2017-03-17-15-26/mm/hugetlb.c v4.11-rc2-mmotm-2017-03-17-15-26_patched/mm/hugetlb.c > index 3d0aab9..f501f14 100644 > --- v4.11-rc2-mmotm-2017-03-17-15-26/mm/hugetlb.c > +++ v4.11-rc2-mmotm-2017-03-17-15-26_patched/mm/hugetlb.c > @@ -4651,6 +4651,7 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, > { > struct page *page = NULL; > spinlock_t *ptl; > + pte_t pte; > retry: > ptl = pmd_lockptr(mm, pmd); > spin_lock(ptl); > @@ -4660,12 +4661,13 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, > */ > if (!pmd_huge(*pmd)) > goto out; > - if (pmd_present(*pmd)) { > + pte = huge_ptep_get((pte_t *)pmd); > + if (pte_present(pte)) { > page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); > if (flags & FOLL_GET) > get_page(page); > } else { > - if (is_hugetlb_entry_migration(huge_ptep_get((pte_t *)pmd))) { > + if (is_hugetlb_entry_migration(pte)) { > spin_unlock(ptl); > __migration_entry_wait(mm, (pte_t *)pmd, ptl); > goto retry; > -- > 2.7.0 -- Michal Hocko SUSE Labs