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Thu, 14 Jun 2018 14:16:19 +0900 From: Naoya Horiguchi To: Michal Hocko CC: "linux-mm@kvack.org" , Pavel Tatashin , Steven Sistare , Daniel Jordan , Oscar Salvador , Matthew Wilcox , "linux-kernel@vger.kernel.org" , Andrew Morton , "mingo@kernel.org" , "dan.j.williams@intel.com" , Huang Ying Subject: Re: [PATCH v1] mm: zero remaining unavailable struct pages (Re: kernel panic in reading /proc/kpageflags when enabling RAM-simulated PMEM) Thread-Topic: [PATCH v1] mm: zero remaining unavailable struct pages (Re: kernel panic in reading /proc/kpageflags when enabling RAM-simulated PMEM) Thread-Index: AQHUAtkgPBcB1vgLY0uIXLgyPjVYAKRdTzQAgAFR3wA= Date: Thu, 14 Jun 2018 05:16:18 +0000 Message-ID: <20180614051618.GB17860@hori1.linux.bs1.fc.nec.co.jp> References: <20180606080408.GA31794@techadventures.net> <20180606085319.GA32052@techadventures.net> <20180606090630.GA27065@hori1.linux.bs1.fc.nec.co.jp> <20180606092405.GA6562@hori1.linux.bs1.fc.nec.co.jp> <20180607062218.GB22554@hori1.linux.bs1.fc.nec.co.jp> <20180607065940.GA7334@techadventures.net> <20180607094921.GA8545@techadventures.net> <20180607100256.GA9129@hori1.linux.bs1.fc.nec.co.jp> <20180613054107.GA5329@hori1.linux.bs1.fc.nec.co.jp> <20180613090700.GG13364@dhcp22.suse.cz> In-Reply-To: <20180613090700.GG13364@dhcp22.suse.cz> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.51.8.81] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-TM-AS-MML: disable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 13, 2018 at 11:07:00AM +0200, Michal Hocko wrote: > On Wed 13-06-18 05:41:08, Naoya Horiguchi wrote: > [...] > > From: Naoya Horiguchi > > Date: Wed, 13 Jun 2018 12:43:27 +0900 > > Subject: [PATCH] mm: zero remaining unavailable struct pages > > > > There is a kernel panic that is triggered when reading /proc/kpageflags > > on the kernel booted with kernel parameter 'memmap=nn[KMG]!ss[KMG]': > > > > BUG: unable to handle kernel paging request at fffffffffffffffe > > PGD 9b20e067 P4D 9b20e067 PUD 9b210067 PMD 0 > > Oops: 0000 [#1] SMP PTI > > CPU: 2 PID: 1728 Comm: page-types Not tainted 4.17.0-rc6-mm1-v4.17-rc6-180605-0816-00236-g2dfb086ef02c+ #160 > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.fc28 04/01/2014 > > RIP: 0010:stable_page_flags+0x27/0x3c0 > > Code: 00 00 00 0f 1f 44 00 00 48 85 ff 0f 84 a0 03 00 00 41 54 55 49 89 fc 53 48 8b 57 08 48 8b 2f 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 01 0f 84 10 03 00 00 31 db 49 8b 54 24 08 4c 89 e7 > > RSP: 0018:ffffbbd44111fde0 EFLAGS: 00010202 > > RAX: fffffffffffffffe RBX: 00007fffffffeff9 RCX: 0000000000000000 > > RDX: 0000000000000001 RSI: 0000000000000202 RDI: ffffed1182fff5c0 > > RBP: ffffffffffffffff R08: 0000000000000001 R09: 0000000000000001 > > R10: ffffbbd44111fed8 R11: 0000000000000000 R12: ffffed1182fff5c0 > > R13: 00000000000bffd7 R14: 0000000002fff5c0 R15: ffffbbd44111ff10 > > FS: 00007efc4335a500(0000) GS:ffff93a5bfc00000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: fffffffffffffffe CR3: 00000000b2a58000 CR4: 00000000001406e0 > > Call Trace: > > kpageflags_read+0xc7/0x120 > > proc_reg_read+0x3c/0x60 > > __vfs_read+0x36/0x170 > > vfs_read+0x89/0x130 > > ksys_pread64+0x71/0x90 > > do_syscall_64+0x5b/0x160 > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > RIP: 0033:0x7efc42e75e23 > > Code: 09 00 ba 9f 01 00 00 e8 ab 81 f4 ff 66 2e 0f 1f 84 00 00 00 00 00 90 83 3d 29 0a 2d 00 00 75 13 49 89 ca b8 11 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 34 c3 48 83 ec 08 e8 db d3 01 00 48 89 04 24 > > > > According to kernel bisection, this problem became visible due to commit > > f7f99100d8d9 which changes how struct pages are initialized. > > > > Memblock layout affects the pfn ranges covered by node/zone. Consider > > that we have a VM with 2 NUMA nodes and each node has 4GB memory, and > > the default (no memmap= given) memblock layout is like below: > > > > MEMBLOCK configuration: > > memory size = 0x00000001fff75c00 reserved size = 0x000000000300c000 > > memory.cnt = 0x4 > > memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0 > > memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0 > > memory[0x2] [0x0000000100000000-0x000000013fffffff], 0x0000000040000000 bytes on node 0 flags: 0x0 > > memory[0x3] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0 > > ... > > > > If you give memmap=1G!4G (so it just covers memory[0x2]), > > the range [0x100000000-0x13fffffff] is gone: > > > > MEMBLOCK configuration: > > memory size = 0x00000001bff75c00 reserved size = 0x000000000300c000 > > memory.cnt = 0x3 > > memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0 > > memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0 > > memory[0x2] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0 > > ... > > > > This causes shrinking node 0's pfn range because it is calculated by > > the address range of memblock.memory. So some of struct pages in the > > gap range are left uninitialized. > > > > We have a function zero_resv_unavail() which does zeroing the struct > > pages outside memblock.memory, but currently it covers only the reserved > > unavailable range (i.e. memblock.memory && !memblock.reserved). > > This patch extends it to cover all unavailable range, which fixes > > the reported issue. > > Thanks for pin pointing this down Naoya! I am wondering why we cannot > simply mark the excluded ranges to be reserved instead. I tried your idea with the change below, and it also fixes the kernel panic. --- diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c index d1f25c831447..2cef120535d4 100644 --- a/arch/x86/kernel/e820.c +++ b/arch/x86/kernel/e820.c @@ -1248,6 +1248,7 @@ void __init e820__memblock_setup(void) { int i; u64 end; + u64 addr = 0; /* * The bootstrap memblock region count maximum is 128 entries @@ -1264,13 +1265,16 @@ void __init e820__memblock_setup(void) struct e820_entry *entry = &e820_table->entries[i]; end = entry->addr + entry->size; + if (addr < entry->addr) + memblock_reserve(addr, entry->addr - addr); + addr = end; if (end != (resource_size_t)end) continue; if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN) - continue; - - memblock_add(entry->addr, entry->size); + memblock_reserve(entry->addr, entry->size); + else + memblock_add(entry->addr, entry->size); } /* Throw away partial pages: */ My concern is that there are a few E820 memory types rather than E820_TYPE_RAM and E820_TYPE_RESERVED, and I'm not sure that putting them all into memblock.reserved is really acceptable. Thanks, Naoya Horiguchi