From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 19 Dec 2018 14:28:13 +0000 From: Wei Yang Subject: Re: [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages Message-ID: <20181219142813.4d6kiuac64lazurd@master> Reply-To: Wei Yang References: <20181217225113.17864-1-osalvador@suse.de> <20181219142528.yx6ravdyzcqp5wtd@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181219142528.yx6ravdyzcqp5wtd@master> Sender: linux-kernel-owner@vger.kernel.org To: Wei Yang Cc: Oscar Salvador , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, pavel.tatashin@microsoft.com, rppt@linux.vnet.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Wed, Dec 19, 2018 at 02:25:28PM +0000, Wei Yang wrote: >On Mon, Dec 17, 2018 at 11:51:13PM +0100, Oscar Salvador wrote: >>v1 -> v2: >> - Fix the logic for skipping pages by Michal >> >>--- >>>>>From e346b151037d3c37feb10a981a4d2a25018acf81 Mon Sep 17 00:00:00 2001 >>From: Oscar Salvador >>Date: Mon, 17 Dec 2018 14:53:35 +0100 >>Subject: [PATCH] mm, page_alloc: Fix has_unmovable_pages for HugePages >> >>While playing with gigantic hugepages and memory_hotplug, I triggered >>the following #PF when "cat memoryX/removable": >> >><--- >>kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 >>kernel: #PF error: [normal kernel read fault] >>kernel: PGD 0 P4D 0 >>kernel: Oops: 0000 [#1] SMP PTI >>kernel: CPU: 1 PID: 1481 Comm: cat Tainted: G E 4.20.0-rc6-mm1-1-default+ #18 >>kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014 >>kernel: RIP: 0010:has_unmovable_pages+0x154/0x210 >>kernel: Code: 1b ff ff ff eb 32 48 8b 45 00 bf 00 10 00 00 a9 00 00 01 00 74 07 0f b6 4d 51 48 d3 e7 e8 c4 81 05 00 48 85 c0 49 89 c1 75 7e <41> 8b 41 08 83 f8 09 74 41 83 f8 1b 74 3c 4d 2b 64 24 58 49 81 ec >>kernel: RSP: 0018:ffffc90000a1fd30 EFLAGS: 00010246 >>kernel: RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000009 >>kernel: RDX: ffffffff82aed4f0 RSI: 0000000000001000 RDI: 0000000000001000 >>kernel: RBP: ffffea0001800000 R08: 0000000000200000 R09: 0000000000000000 >>kernel: R10: 0000000000001000 R11: 0000000000000003 R12: ffff88813ffd45c0 >>kernel: R13: 0000000000060000 R14: 0000000000000001 R15: ffffea0000000000 >>kernel: FS: 00007fd71d9b3500(0000) GS:ffff88813bb00000(0000) knlGS:0000000000000000 >>kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>kernel: CR2: 0000000000000008 CR3: 00000001371c2002 CR4: 00000000003606e0 >>kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>kernel: Call Trace: >>kernel: is_mem_section_removable+0x7d/0x100 >>kernel: removable_show+0x90/0xb0 >>kernel: dev_attr_show+0x1c/0x50 >>kernel: sysfs_kf_seq_show+0xca/0x1b0 >>kernel: seq_read+0x133/0x380 >>kernel: __vfs_read+0x26/0x180 >>kernel: vfs_read+0x89/0x140 >>kernel: ksys_read+0x42/0x90 >>kernel: do_syscall_64+0x5b/0x180 >>kernel: entry_SYSCALL_64_after_hwframe+0x44/0xa9 >>kernel: RIP: 0033:0x7fd71d4c8b41 >>kernel: Code: fe ff ff 48 8d 3d 27 9e 09 00 48 83 ec 08 e8 96 02 02 00 66 0f 1f 44 00 00 8b 05 ea fc 2c 00 48 63 ff 85 c0 75 13 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 57 f3 c3 0f 1f 44 00 00 55 53 48 89 d5 48 89 >>kernel: RSP: 002b:00007ffeab5f6448 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 >>kernel: RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007fd71d4c8b41 >>kernel: RDX: 0000000000020000 RSI: 00007fd71d809000 RDI: 0000000000000003 >>kernel: RBP: 0000000000020000 R08: ffffffffffffffff R09: 0000000000000000 >>kernel: R10: 000000000000038b R11: 0000000000000246 R12: 00007fd71d809000 >>kernel: R13: 0000000000000003 R14: 00007fd71d80900f R15: 0000000000020000 >>kernel: Modules linked in: af_packet(E) xt_tcpudp(E) ipt_REJECT(E) xt_conntrack(E) nf_conntrack(E) nf_defrag_ipv4(E) ip_set(E) nfnetlink(E) ebtable_nat(E) ebtable_broute(E) bridge(E) stp(E) llc(E) iptable_mangle(E) iptable_raw(E) iptable_security(E) ebtable_filter(E) ebtables(E) iptable_filter(E) ip_tables(E) x_tables(E) kvm_intel(E) kvm(E) irqbypass(E) crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E) bochs_drm(E) ttm(E) drm_kms_helper(E) drm(E) aesni_intel(E) virtio_net(E) syscopyarea(E) net_failover(E) sysfillrect(E) failover(E) aes_x86_64(E) crypto_simd(E) sysimgblt(E) cryptd(E) pcspkr(E) glue_helper(E) parport_pc(E) fb_sys_fops(E) i2c_piix4(E) parport(E) button(E) btrfs(E) libcrc32c(E) xor(E) zstd_decompress(E) zstd_compress(E) raid6_pq(E) sd_mod(E) ata_generic(E) ata_piix(E) ahci(E) libahci(E) serio_raw(E) crc32c_intel(E) virtio_pci(E) virtio_ring(E) virtio(E) libata(E) sg(E) scsi_mod(E) autofs4(E) >>kernel: CR2: 0000000000000008 >>kernel: ---[ end trace 49cade81474e40e7 ]--- >>kernel: RIP: 0010:has_unmovable_pages+0x154/0x210 >>kernel: Code: 1b ff ff ff eb 32 48 8b 45 00 bf 00 10 00 00 a9 00 00 01 00 74 07 0f b6 4d 51 48 d3 e7 e8 c4 81 05 00 48 85 c0 49 89 c1 75 7e <41> 8b 41 08 83 f8 09 74 41 83 f8 1b 74 3c 4d 2b 64 24 58 49 81 ec >>kernel: RSP: 0018:ffffc90000a1fd30 EFLAGS: 00010246 >>kernel: RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000009 >>kernel: RDX: ffffffff82aed4f0 RSI: 0000000000001000 RDI: 0000000000001000 >>kernel: RBP: ffffea0001800000 R08: 0000000000200000 R09: 0000000000000000 >>kernel: R10: 0000000000001000 R11: 0000000000000003 R12: ffff88813ffd45c0 >>kernel: R13: 0000000000060000 R14: 0000000000000001 R15: ffffea0000000000 >>kernel: FS: 00007fd71d9b3500(0000) GS:ffff88813bb00000(0000) knlGS:0000000000000000 >>kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>kernel: CR2: 0000000000000008 CR3: 00000001371c2002 CR4: 00000000003606e0 >>kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>---> >> >>The reason is we do not pass the Head to page_hstate(), and so, >>the call to compound_order() in page_hstate() returns 0, so >>we end up checking all hstates's size to match PAGE_SIZE. >> >>Obviously, we do not find any hstate matching that size, and we >>return NULL. >>Then, we dereference that NULL pointer in hugepage_migration_supported() >>and we got the #PF from above. >> >>Fix that by getting the head page before calling page_hstate(). >> >>Also, since gigantic pages span several pageblocks, re-adjust the logic >>for skipping pages. >> >>Signed-off-by: Oscar Salvador >>--- >> mm/page_alloc.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >>diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>index a6e7bfd18cde..90ad281f750c 100644 >>--- a/mm/page_alloc.c >>+++ b/mm/page_alloc.c >>@@ -8038,11 +8038,14 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, >> * handle each tail page individually in migration. >> */ >> if (PageHuge(page)) { >>+ struct page *head = compound_head(page); >>+ unsigned int skip_pages; >> >>- if (!hugepage_migration_supported(page_hstate(page))) >>+ if (!hugepage_migration_supported(page_hstate(head))) >> goto unmovable; >> >>- iter = round_up(iter + 1, 1<>+ skip_pages = (1 << compound_order(head)) - (page - head); >>+ iter = round_up(iter + 1, skip_pages) - 1; > >The comment of round_up says round up to next specified power of 2. And >second parameter must be a power of 2. > >Look skip_pages not satisfy this. > Maybe the first version from Oscar is correct, because round_up() does the (page - head) calculation in it. >> continue; >> } >> >>-- >>2.13.7 > >-- >Wei Yang >Help you, Help me -- Wei Yang Help you, Help me