Re: [BUG] kernel BUG at drivers/block/xen-blkfront.c:1711

[Bob Liu <bob.liu@oracle.com>]

On 07/11/2016 04:50 PM, Evgenii Shatokhin wrote:
> On 06.06.2016 11:42, Dario Faggioli wrote:
>> Just Cc-ing some Linux, block, and Xen on CentOS people...
>>
> 
> Ping.
> 
> Any suggestions how to debug this or what might cause the problem?
> 
> Obviously, we cannot control Xen on the Amazon's servers. But perhaps there is something we can do at the kernel's side, is it?
> 
>> On Mon, 2016-06-06 at 11:24 +0300, Evgenii Shatokhin wrote:
>>> (Resending this bug report because the message I sent last week did
>>> not
>>> make it to the mailing list somehow.)
>>>
>>> Hi,
>>>
>>> One of our users gets kernel panics from time to time when he tries
>>> to
>>> use his Amazon EC2 instance with CentOS7 x64 in it [1]. Kernel panic
>>> happens within minutes from the moment the instance starts. The
>>> problem
>>> does not show up every time, however.
>>>
>>> The user first observed the problem with a custom kernel, but it was
>>> found later that the stock kernel 3.10.0-327.18.2.el7.x86_64 from
>>> CentOS7 was affected as well.

Please try this patch:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7b0767502b5db11cb1f0daef2d01f6d71b1192dc

Regards,
Bob

>>>
>>> The part of the system log he was able to retrieve is attached. Here
>>> is
>>> the bug info, for convenience:
>>>
>>> ------------------------------------
>>> [    2.246912] kernel BUG at drivers/block/xen-blkfront.c:1711!
>>> [    2.246912] invalid opcode: 0000 [#1] SMP
>>> [    2.246912] Modules linked in: ata_generic pata_acpi
>>> crct10dif_pclmul
>>> crct10dif_common crc32_pclmul crc32c_intel ghash_clmulni_intel
>>> xen_netfront xen_blkfront(+) aesni_intel lrw ata_piix gf128mul
>>> glue_helper ablk_helper cryptd libata serio_raw floppy sunrpc
>>> dm_mirror
>>> dm_region_hash dm_log dm_mod scsi_transport_iscsi
>>> [    2.246912] CPU: 1 PID: 50 Comm: xenwatch Not tainted
>>> 3.10.0-327.18.2.el7.x86_64 #1
>>> [    2.246912] Hardware name: Xen HVM domU, BIOS 4.2.amazon
>>> 12/07/2015
>>> [    2.246912] task: ffff8800e9fcb980 ti: ffff8800e98bc000 task.ti:
>>> ffff8800e98bc000
>>> [    2.246912] RIP: 0010:[<ffffffffa015584f>]  [<ffffffffa015584f>]
>>> blkfront_setup_indirect+0x41f/0x430 [xen_blkfront]
>>> [    2.246912] RSP: 0018:ffff8800e98bfcd0  EFLAGS: 00010283
>>> [    2.246912] RAX: ffff8800353e15c0 RBX: ffff8800e98c52c8 RCX:
>>> 0000000000000020
>>> [    2.246912] RDX: ffff8800353e15b0 RSI: ffff8800e98c52b8 RDI:
>>> ffff8800353e15d0
>>> [    2.246912] RBP: ffff8800e98bfd20 R08: ffff8800353e15b0 R09:
>>> ffff8800eb403c00
>>> [    2.246912] R10: ffffffffa0155532 R11: ffffffffffffffe8 R12:
>>> ffff8800e98c4000
>>> [    2.246912] R13: ffff8800e98c52b8 R14: 0000000000000020 R15:
>>> ffff8800353e15c0
>>> [    2.246912] FS:  0000000000000000(0000) GS:ffff8800efc20000(0000)
>>> knlGS:0000000000000000
>>> [    2.246912] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [    2.246912] CR2: 00007f1b615ef000 CR3: 00000000e2b44000 CR4:
>>> 00000000001406e0
>>> [    2.246912] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
>>> 0000000000000000
>>> [    2.246912] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
>>> 0000000000000400
>>> [    2.246912] Stack:
>>> [    2.246912]  0000000000000020 0000000000000001 00000020a0157217
>>> 00000100e98bfdbc
>>> [    2.246912]  0000000027efa3ef ffff8800e98bfdbc ffff8800e98ce000
>>> ffff8800e98c4000
>>> [    2.246912]  ffff8800e98ce040 0000000000000001 ffff8800e98bfe08
>>> ffffffffa0155d4c
>>> [    2.246912] Call Trace:
>>> [    2.246912]  [<ffffffffa0155d4c>] blkback_changed+0x4ec/0xfc8
>>> [xen_blkfront]
>>> [    2.246912]  [<ffffffff813a6fd0>] ? xenbus_gather+0x170/0x190
>>> [    2.246912]  [<ffffffff816322f5>] ? __slab_free+0x10e/0x277
>>> [    2.246912]  [<ffffffff813a805d>]
>>> xenbus_otherend_changed+0xad/0x110
>>> [    2.246912]  [<ffffffff813a7257>] ? xenwatch_thread+0x77/0x180
>>> [    2.246912]  [<ffffffff813a9ba3>] backend_changed+0x13/0x20
>>> [    2.246912]  [<ffffffff813a7246>] xenwatch_thread+0x66/0x180
>>> [    2.246912]  [<ffffffff810a6ae0>] ? wake_up_atomic_t+0x30/0x30
>>> [    2.246912]  [<ffffffff813a71e0>] ?
>>> unregister_xenbus_watch+0x1f0/0x1f0
>>> [    2.246912]  [<ffffffff810a5aef>] kthread+0xcf/0xe0
>>> [    2.246912]  [<ffffffff810a5a20>] ?
>>> kthread_create_on_node+0x140/0x140
>>> [    2.246912]  [<ffffffff81646118>] ret_from_fork+0x58/0x90
>>> [    2.246912]  [<ffffffff810a5a20>] ?
>>> kthread_create_on_node+0x140/0x140
>>> [    2.246912] Code: e1 48 85 c0 75 ce 49 8d 84 24 40 01 00 00 48 89
>>> 45
>>> b8 e9 91 fd ff ff 4c 89 ff e8 8d ae 06 e1 e9 f2 fc ff ff 31 c0 e9 2e
>>> fe
>>> ff ff <0f> 0b e8 9a 57 f2 e0 0f 0b 0f 1f 84 00 00 00 00 00 0f 1f 44
>>> 00
>>> [    2.246912] RIP  [<ffffffffa015584f>]
>>> blkfront_setup_indirect+0x41f/0x430 [xen_blkfront]
>>> [    2.246912]  RSP <ffff8800e98bfcd0>
>>> [    2.491574] ---[ end trace 8a9b992812627c71 ]---
>>> [    2.495618] Kernel panic - not syncing: Fatal exception
>>> ------------------------------------
>>>
>>> Xen version 4.2.
>>>
>>> EC2 instance type: c3.large with EBS magnetic storage, if that
>>> matters.
>>>
>>> Here is the code where the BUG_ON triggers (drivers/block/xen-
>>> blkfront.c):
>>> ------------------------------------
>>> if (!info->feature_persistent && info->max_indirect_segments) {
>>>       /*
>>>           * We are using indirect descriptors but not persistent
>>>           * grants, we need to allocate a set of pages that can be
>>>           * used for mapping indirect grefs
>>>           */
>>>       int num = INDIRECT_GREFS(segs) * BLK_RING_SIZE;
>>>
>>>       BUG_ON(!list_empty(&info->indirect_pages)); // << This one hits.
>>>       for (i = 0; i < num; i++) {
>>>           struct page *indirect_page = alloc_page(GFP_NOIO);
>>>           if (!indirect_page)
>>>               goto out_of_memory;
>>>           list_add(&indirect_page->lru, &info->indirect_pages);
>>>       }
>>> }
>>> ------------------------------------
>>>
>>> As we checked, 'info->indirect_pages' list indeed contained around
>>> 30
>>> elements at that point.
>>>
>>> Any ideas what may cause this and how to fix it?
>>>
>>> If any other data are needed, please let me know.
>>>
>>> References:
>>> [1] https://bugs.openvz.org/browse/OVZ-6718

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