From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net ([212.227.17.20]:65082 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752596AbbIVIkY (ORCPT ); Tue, 22 Sep 2015 04:40:24 -0400 Subject: Re: kernel BUG at linux-4.2.0/fs/btrfs/extent-tree.c:1833 on rebalance To: =?UTF-8?Q?St=c3=a9phane_Lesimple?= , Qu Wenruo References: <9c864637fe7676a8b7badc5ddd7a4e0c@all.all> <55F9486F.4040302@googlemail.com> <0973de930ee87e102c533c719807b748@all.all> <55FA2D9A.1060405@cn.fujitsu.com> <55FA60C5.5090002@cn.fujitsu.com> <7a6f2d794fb6cbf7d598b92e3470201c@all.all> <55FA759E.6030707@cn.fujitsu.com> <3386a8bfa1a5796460306a53a668e47e@all.all> <55FA98D8.5010301@gmx.com> <53a5553a9c5301789e246144bb264e43@all.all> <55FB61E9.4000300@cn.fujitsu.com> <2ce9b35f73732b145e0f80b18f230a52@all.all> <762ec73d5389b5057be4d3c17f74e1f9@all.all> <55FE0A50.9060607@gmx.com> <3ba27cf5afd82cf4e3bde718386b7cc3@all.all> <55FE8FB6.4070509@gmx.com> <72b4368e7180a4d703ef3ea1112d7358@all.all> <4749d42363070fcd228af172781750df@all.all> <5600B0BF.604@cn.fujitsu.com> <0a4be8fab4876a245900e4833e8139e0@all.all> Cc: linux-btrfs@vger.kernel.org From: Qu Wenruo Message-ID: <560113EF.2090209@gmx.com> Date: Tue, 22 Sep 2015 16:40:15 +0800 MIME-Version: 1.0 In-Reply-To: <0a4be8fab4876a245900e4833e8139e0@all.all> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: 在 2015年09月22日 15:34, Stéphane Lesimple 写道: > Le 2015-09-22 03:37, Qu Wenruo a écrit : >> Stéphane Lesimple wrote on 2015/09/22 03:30 +0200: >>> Le 2015-09-20 13:14, Stéphane Lesimple a écrit : >>>> Le 2015-09-20 12:51, Qu Wenruo a écrit : >>>>>>> Would you please use gdb to show the codes of >>>>>>> "btrfs_qgroup_rescan_worker+0x388" ? >>>>>>> (Need kernel debuginfo) >>>>>>> >>>>>>> My guess is the following line:(pretty sure, but not 100% sure) >>>>>>> ------ >>>>>>> /* >>>>>>> * only update status, since the previous part has alreay >>>>>>> updated the >>>>>>> * qgroup info. >>>>>>> */ >>>>>>> trans = btrfs_start_transaction(fs_info->quota_root, 1); >>>>>>> <<<<< >>>>>>> if (IS_ERR(trans)) { >>>>>>> err = PTR_ERR(trans); >>>>>>> btrfs_err(fs_info, >>>>>>> "fail to start transaction for status >>>>>>> update: %d\n", >>>>>>> err); >>>>>>> goto done; >>>>>>> } >>>>>>> ------ >>>>>> >>>>>> The kernel and modules were already compiled with debuginfo. >>>>>> However for some reason, I couldn't get gdb disassembly of >>>>>> /proc/kcore >>>>>> properly >>>>>> aligned with the source I compiled: the asm code doesn't match the C >>>>>> code shown >>>>>> by gdb. In any case, watching the source of this function, this is >>>>>> the >>>>>> only place >>>>>> btrfs_start_transaction is called, so we can be 100% sure it's where >>>>>> the >>>>>> crash >>>>>> happens indeed. >>>>> >>>>> Yep, that's the only caller. >>>>> >>>>> Here is some useful small hint to locate the code, if you are >>>>> interestied in kernel development. >>>>> >>>>> # Not sure about whether ubuntu gzipped modules, at least Arch does >>>>> # compress it >>>>> $ cp /kernel/fs/btrfs/btrfs.ko.gz /tmp/ >>>>> $ gunzip /tmp/btrfs.ko.gz >>>>> $ gdb /tmp/btrfs.ko >>>>> # Make sure gdb read all the needed debuginfo >>>>> $ gdb list *(btrfs_qgroup_rescan_worker+0x388) >>>>> >>>>> And gdb will find the code position for you. >>>>> Quite easy one, only backtrace info is needed. >>>> >>>> Ah, thanks for the tips, I was loading whole vmlinux and using >>>> /proc/kcore >>>> as the core info, then adding the module with "add-symbol-file". But as >>>> we're just looking for the code and not the variables, it was indeed >>>> completely overkill. >>>> >>>> (gdb) list *(btrfs_qgroup_rescan_worker+0x388) >>>> 0x98068 is in btrfs_qgroup_rescan_worker (fs/btrfs/qgroup.c:2328). >>>> 2323 >>>> 2324 /* >>>> 2325 * only update status, since the previous part has >>>> alreay updated the >>>> 2326 * qgroup info. >>>> 2327 */ >>>> 2328 trans = btrfs_start_transaction(fs_info->quota_root, >>>> 1); >>>> 2329 if (IS_ERR(trans)) { >>>> 2330 err = PTR_ERR(trans); >>>> 2331 btrfs_err(fs_info, >>>> 2332 "fail to start transaction for >>>> status update: %d\n", >>>> >>>> So this just confirms what we were already 99% sure of. >>>> >>>>> Another hint is about how to collect the kernel crash info. >>>>> Your netconsole setup would be definitely one good practice. >>>>> >>>>> Another one I use to collect crash info is kdump. >>>>> Ubuntu should have a good wiki on it. >>>> >>>> I've already come across kdump a few times, but never really look into >>>> it. >>>> To debug the other complicated extend backref bug, it could be of some >>>> use. >>>> >>>>>>>>> So, as a quick summary of this big thread, it seems I've been >>>>>>>>> hitting >>>>>>>>> 3 bugs, all reproductible : >>>>>>>>> - kernel BUG on balance (this original thread) >>>>>>> >>>>>>> For this, I can't provide much help, as extent backref bug is quite >>>>>>> hard to debug, unless a developer is interested in it and find a >>>>>>> stable way to reproduce it. >>>>>> >>>>>> Yes, unfortunately as it looks so much like a race condition, I know >>>>>> I can >>>>>> reproduce it with my worflow, but it can take between 1 minute and 12 >>>>>> hours, >>>>>> so I wouldn't call it a "stable way" to reproduce it unfortunately :( >>>>>> >>>>>> Still if any dev is interested in it, I can reproduce it, with a >>>>>> patched >>>>>> kernel if needed. >>>>> >>>>> Maybe you are already doing it, you can only compile the btrfs >>>>> modules, which will be far more faster than compile the whole kernel, >>>>> if and only if the compiled module can be loaded. >>>> >>>> Yes, I've compiled this 4.3.0-rc1 in a completely modular form, so >>>> I'll try to >>>> load the modified module and see if the running kernel accepts it. I >>>> have to rmmod >>>> the loaded module first, hence umounting any btrfs fs before that. >>>> Should be able >>>> to do it in a couple hours. >>>> >>>> I'll delete again all my snapshots and run my script. Should be easy >>>> to trigger >>>> the (hopefully worked-around) bug again. >>> >>> Well, I didn't trigger this exact bug, but another one, not less severe >>> though, as it also crashed the system: >>> >>> [92098.841309] general protection fault: 0000 [#1] SMP >>> [92098.841338] Modules linked in: ... >>> [92098.841814] CPU: 1 PID: 24655 Comm: kworker/u4:12 Not tainted >>> 4.3.0-rc1 #1 >>> [92098.841834] Hardware name: ASUS All Series/H87I-PLUS, BIOS 1005 >>> 01/06/2014 >>> [92098.841868] Workqueue: btrfs-qgroup-rescan btrfs_qgroup_rescan_helper >>> [btrfs] >>> [92098.841889] task: ffff8800b6cc4100 ti: ffff8800a3dc8000 task.ti: >>> ffff8800a3dc8000 >>> [92098.841910] RIP: 0010:[] [] >>> memcpy_erms+0x6/0x10 >>> [92098.841935] RSP: 0018:ffff8800a3dcbcc8 EFLAGS: 00010207 >>> [92098.841950] RAX: ffff8800a3dcbd67 RBX: 0000000000000009 RCX: >>> 0000000000000009 >>> [92098.841970] RDX: 0000000000000009 RSI: 0005080000000000 RDI: >>> ffff8800a3dcbd67 >>> [92098.841989] RBP: ffff8800a3dcbd00 R08: 0000000000019c60 R09: >>> ffff88011fb19c60 >>> [92098.842009] R10: ffffea0003006480 R11: 0000000001000000 R12: >>> ffff8800b76c32c0 >>> [92098.842028] R13: 0000160000000000 R14: ffff8800a3dcbd70 R15: >>> 0000000000000009 >>> [92098.842048] FS: 0000000000000000(0000) GS:ffff88011fb00000(0000) >>> knlGS:0000000000000000 >>> [92098.842070] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [92098.842086] CR2: 00007fe1f2bd8000 CR3: 0000000001c10000 CR4: >>> 00000000000406e0 >>> [92098.842105] Stack: >>> [92098.842111] ffffffffc035a5d8 ffffffffc0396d00 000000000000028b >>> 0000000000000000 >>> [92098.842212] 0000cc6c00000000 ffff8800b76c3200 0000160000000000 >>> ffff8800a3dcbdc0 >>> [92098.842237] ffffffffc039af3d ffff8800c7196dc8 ffff8800c7196e08 >>> ffff8800c7196da0 >>> [92098.842261] Call Trace: >>> [92098.842277] [] ? read_extent_buffer+0xb8/0x110 >>> [btrfs] >>> [92098.842304] [] ? btrfs_find_all_roots+0x60/0x70 >>> [btrfs] >>> [92098.842329] [] >>> btrfs_qgroup_rescan_worker+0x28d/0x5a0 [btrfs] >> >> Would you please show the code of it? >> This one seems to be another stupid bug I made when rewriting the >> framework. >> Maybe I forgot to reinit some variants or I'm screwing memory... > > (gdb) list *(btrfs_qgroup_rescan_worker+0x28d) > 0x97f6d is in btrfs_qgroup_rescan_worker (fs/btrfs/ctree.h:2760). > 2755 > 2756 static inline void btrfs_disk_key_to_cpu(struct btrfs_key *cpu, > 2757 struct btrfs_disk_key > *disk) > 2758 { > 2759 cpu->offset = le64_to_cpu(disk->offset); > 2760 cpu->type = disk->type; > 2761 cpu->objectid = le64_to_cpu(disk->objectid); > 2762 } > 2763 > 2764 static inline void btrfs_cpu_key_to_disk(struct btrfs_disk_key > *disk, > (gdb) > > > Does it makes sense ? So it seems that the memory of cpu key is being screwed up... The code is be specific thin inline function, so what about other stack? Like btrfs_qgroup_rescan_helper+0x12? Thanks, Qu > > >>> [92098.842351] [] ? >>> ttwu_do_activate.constprop.90+0x5d/0x70 >>> [92098.842377] [] normal_work_helper+0xc0/0x270 >>> [btrfs] >>> [92098.842401] [] >>> btrfs_qgroup_rescan_helper+0x12/0x20 [btrfs] >>> [92098.842421] [] process_one_work+0x14e/0x3d0 >>> [92098.842438] [] worker_thread+0x11a/0x470 >>> [92098.842454] [] ? rescuer_thread+0x310/0x310 >>> [92098.842471] [] kthread+0xc9/0xe0 >>> [92098.842485] [] ? kthread_park+0x60/0x60 >>> [92098.842502] [] ret_from_fork+0x3f/0x70 >>> [92098.842517] [] ? kthread_park+0x60/0x60 >>> [92098.842532] Code: ff eb eb 90 90 eb 1e 0f 1f 00 48 89 f8 48 89 d1 48 >>> c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 >>> 89 d1 a4 c3 0f 1f 80 00 00 00 00 48 89 f8 48 83 fa 20 72 7e 40 38 >>> [92098.842658] RIP [] memcpy_erms+0x6/0x10 >>> [92098.842675] RSP >>> [92098.849594] ---[ end trace 9d5fb7931a3ec713 ]--- >>> >>> I would definitely say that rescans should be avoided on current kernels >>> as the possibility that it'll bring the system down shouldn't be >>> ignored. >>> It confirms that this code really needs a rewrite ! >>> >>> Regards, >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >