From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x22f.google.com (mail-wm0-x22f.google.com [IPv6:2a00:1450:400c:c09::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 6DAA51A03EF for ; Thu, 18 Feb 2016 10:58:16 +1100 (AEDT) Received: by mail-wm0-x22f.google.com with SMTP id g62so2100632wme.1 for ; Wed, 17 Feb 2016 15:58:16 -0800 (PST) Date: Thu, 18 Feb 2016 01:58:08 +0200 From: "Kirill A. Shutemov" To: Gerald Schaefer Cc: Sebastian Ott , Andrea Arcangeli , Christian Borntraeger , "Kirill A. Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Aneesh Kumar K.V" , Andrew Morton , Linus Torvalds , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, Martin Schwidefsky , Heiko Carstens , linux-s390@vger.kernel.org Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) Message-ID: <20160217235808.GA21696@node.shutemov.name> References: <20160211192223.4b517057@thinkpad> <20160211190942.GA10244@node.shutemov.name> <20160211205702.24f0d17a@thinkpad> <20160212154116.GA15142@node.shutemov.name> <56BE00E7.1010303@de.ibm.com> <20160212181640.4eabb85f@thinkpad> <20160212231510.GB15142@node.shutemov.name> <20160217201340.2dafad8d@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160217201340.2dafad8d@thinkpad> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Feb 17, 2016 at 08:13:40PM +0100, Gerald Schaefer wrote: > On Sat, 13 Feb 2016 12:58:31 +0100 (CET) > Sebastian Ott wrote: > > > [ 59.875935] ------------[ cut here ]------------ > > [ 59.875937] kernel BUG at mm/huge_memory.c:2884! > > [ 59.875979] illegal operation: 0001 ilc:1 [#1] PREEMPT SMP DEBUG_PAGEALLOC > > [ 59.875986] Modules linked in: bridge stp llc btrfs xor mlx4_en vxlan ip6_udp_tunnel udp_tunnel mlx4_ib ptp pps_core ib_sa ib_mad ib_core ib_addr ghash_s390 prng raid6_pq ecb aes_s390 des_s390 des_generic sha512_s390 sha256_s390 sha1_s390 mlx4_core sha_common genwqe_card scm_block crc_itu_t vhost_net tun vhost dm_mod macvtap eadm_sch macvlan kvm autofs4 > > [ 59.876033] CPU: 2 PID: 5402 Comm: git Tainted: G W 4.4.0-07794-ga4eff16-dirty #77 > > [ 59.876036] task: 00000000d2312948 ti: 00000000cfecc000 task.ti: 00000000cfecc000 > > [ 59.876039] Krnl PSW : 0704d00180000000 00000000002bf3aa (__split_huge_pmd_locked+0x562/0xa10) > > [ 59.876045] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 EA:3 > > Krnl GPRS: 0000000001a7a1cf 000003d10177c000 0000000000044068 000000005df00215 > > [ 59.876051] 0000000000000001 0000000000000001 0000000000000000 00000000774e6900 > > [ 59.876054] 000003ff52000000 000000006d403b10 000000006e1eb800 000003ff51f00000 > > [ 59.876058] 000003d10177c000 0000000000715190 00000000002bf234 00000000cfecfb58 > > [ 59.876068] Krnl Code: 00000000002bf39c: d507d010a000 clc 16(8,%%r13),0(%%r10) > > 00000000002bf3a2: a7840004 brc 8,2bf3aa > > #00000000002bf3a6: a7f40001 brc 15,2bf3a8 > > >00000000002bf3aa: 91407440 tm 1088(%%r7),64 > > 00000000002bf3ae: a7840208 brc 8,2bf7be > > 00000000002bf3b2: a7f401e9 brc 15,2bf784 > > 00000000002bf3b6: 9104a006 tm 6(%%r10),4 > > 00000000002bf3ba: a7740004 brc 7,2bf3c2 > > [ 59.876089] Call Trace: > > [ 59.876092] ([<00000000002bf234>] __split_huge_pmd_locked+0x3ec/0xa10) > > [ 59.876095] [<00000000002c4310>] __split_huge_pmd+0x118/0x218 > > [ 59.876099] [<00000000002810e8>] unmap_single_vma+0x2d8/0xb40 > > [ 59.876102] [<0000000000282d66>] zap_page_range+0x116/0x318 > > [ 59.876105] [<000000000029b834>] SyS_madvise+0x23c/0x5e8 > > [ 59.876108] [<00000000006f9f56>] system_call+0xd6/0x258 > > [ 59.876111] [<000003ff9bbfd282>] 0x3ff9bbfd282 > > [ 59.876113] INFO: lockdep is turned off. > > [ 59.876115] Last Breaking-Event-Address: > > [ 59.876118] [<00000000002bf3a6>] __split_huge_pmd_locked+0x55e/0xa10 > > The BUG at mm/huge_memory.c:2884 is interesting, it's the BUG_ON(!pte_none(*pte)) > check in __split_huge_pmd_locked(). Obviously we expect the pre-allocated > pagetables to be empty, but in collapse_huge_page() we deposit the original > pagetable instead of allocating a new (empty) one. This saves an allocation, > which is good, but doesn't that mean that if such a collapsed hugepage will > ever be split, we will always run into the BUG_ON(!pte_none(*pte)), or one > of the two other VM_BUG_ONs in mm/huge_memory.c that check the same? > > This behavior is not new, it was the same before the THP rework, so I do not > assume that it is related to the current problems, maybe with the exception > of this specific crash. I never saw the BUG at mm/huge_memory.c:2884 myself, > and the other crashes probably cannot be explained with this. Maybe I am > also missing something, but I do not see how collapse_huge_page() and the > (non-empty) pgtable deposit there can work out with the BUG_ON(!pte_none(*pte)) > checks. Any thoughts? I don't think there's a problem: ptes in the pgtable are cleared with pte_clear() in __collapse_huge_page_copy(). -- Kirill A. Shutemov