From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.virtall.com ([178.63.195.102]:58167 "EHLO mail.virtall.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751101AbbFKLdo (ORCPT ); Thu, 11 Jun 2015 07:33:44 -0400 Received: from mailext.virtall.com (localhost [127.0.0.1]) by mailext.virtall.com (Postfix) with ESMTP id D9E693569D7 for ; Thu, 11 Jun 2015 13:33:41 +0200 (CEST) To: linux-btrfs Subject: kernel crashes with btrfs and busy database IO - how to debug? MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Date: Thu, 11 Jun 2015 20:33:41 +0900 From: Tomasz Chmielewski Message-ID: Sender: linux-btrfs-owner@vger.kernel.org List-ID: I have a server where I've installed a couple of LXC guests, btrfs - so easy to test things with snapshots. Or so it seems. Unfortunately the box crashes when I put "too much IO load" - with too much load being these two running at the same time: - quite busy MySQL database (doing up to 100% IO wait when running alone) - busy mongo database (doing up to 100% IO wait when running alone) With both mongo and mysql running at the same time, it crashes after 1-2 days (tried kernels 4.0.4, 4.0.5, 4.1-rc7 from Ubuntu "kernel-ppa"). It does not crash if I only run mongo, or only mysql. There is plenty of memory available (just around 2-4 GB used out of 32 GB) when it crashes. As the box is only reachable remotely, I'm not able to catch a crash. Sometimes, I'm able to get a bit of it printed via remote SSH, like here: [162276.341030] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [162276.341069] IP: [] prepare_to_wait_event+0xcd/0x100 [162276.341096] PGD 80a15e067 PUD 6e08c2067 PMD 0 [162276.341116] Oops: 0002 [#1] SMP [162276.341133] Modules linked in: xfs libcrc32c xt_conntrack veth xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack xt_tcpudp iptable_filter ip_tables x_tables bridge stp llc intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 lrw eeepc_wmi gf128mul asus_wmi glue_helper sparse_keymap ablk_helper cryptd ie31200_edac shpchp lpc_ich edac_core mac_hid 8250_fintek tpm_infineon wmi serio_raw video lp parport btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq e1000e raid1 raid0 ahci ptp libahci multipath pps_core linear [last unloaded: xfs] [162276.341394] CPU: 6 PID: 12853 Comm: mysqld Not tainted 4.1.0-040100rc7-generic #201506080035 [162276.341428] Hardware name: System manufacturer System Product Name/P8B WS, BIOS 0904 10/24/2011 [162276.341463] task: ffff8800730d8a10 ti: ffff88047a0f8000 task.ti: ffff88047a0f8000 [162276.341495] RIP: 0010:[] [] prepare_to_wait_event+0xcd/0x100 [162276.341532] RSP: 0018:ffff88047a0fbcd8 EFLAGS: 00010046 [162276.341583] RDX: ffff88047a0fbd48 RSI: ffff8800730d8a10 RDI: ffff8801e2f96ee8 [162276.341615] RBP: ffff88047a0fbd08 R08: 0000000000000000 R09: 0000000000000001 [162276.341646] R10: 0000000000000001 R11: 0000000000000000 R12: ffff8801e2f96ee8 [162276.341678] R13: 0000000000000002 R14: ffff8801e2f96e60 R15: ffff8806b513f248 [162276.341709] FS: 00007f9f2bbd3700(0000) GS:ffff88082fb80000(0000) knlGS:0000000000000000 Remote syslog does not capture anything. The above crash does not point at btrfs - although the box does not crash with the same tests done on ext4. The box passes memtests and is generally stable otherwise. How can I debug this further? "prepare_to_wait_event" can be found here in 4.1-rc7 kernel: include/linux/wait.h: long __int = prepare_to_wait_event(&wq, &__wait, state);\ include/linux/wait.h:long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state); kernel/sched/wait.c:long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state) kernel/sched/wait.c:EXPORT_SYMBOL(prepare_to_wait_event); -- Tomasz Chmielewski http://wpkg.org