> On Aug 15, 2017, at 2:24 AM, Guoqing Jiang <gqjiang@xxxxxxxx> wrote:
>
>
>
> On 08/14/2017 01:29 AM, Stephane Thiell wrote:
>> Also known as "kernel BUG at drivers/md/raid5.c:527!"
>>
>> I’m still struggling with this issue in raid5.c. I currently have one crash per week in average on a system using Lustre and 24 x 10-disk raid6 per server. It did happen with or without check running. I now think there is a race at some point where a released stripe head (batched) is added to conf->inactive_list without sh->batch_head being set back to NULL.
>>
>> Because sh->batch_head is only being set back to NULL in a single function, break_stripe_batch_list(), my guess is that a call to raid5_release_stripe() on the head stripe is performed elsewhere. I didn’t find where this could come from yet. So perhaps sh->batch_head should be just set to NULL in do_release_stripe(), before being added to the inactive list?
>>
>> Alternatively, I wonder if it would make more sense to set batch_head to NULL where sh->overwrite_disks is also set back to 0 (like in ops_run_biodrain() today).
>>
>> Because sh->overwrite_disks is also set to 0 in init_stripe(), my current plan is to try this change, at least as a workaround: remove the BUG_ON(sh->batch_head) from init_stripe() and set sh->batch_head = NULL (I don’t think I need to lock on sh->stripe_lock there?). I will get new hardware soon so I will give it a try on a test system. Any suggestions welcomed…
>>
>> Quick analysis of the last vmcore:
>>
>> crash> ps | grep ">"
>> ...
>>> 16119 16111 22 ffff881f93bace70 RU 0.0 150772 10748 e2label
>>> 151448 2 34 ffff881ff753bec0 RU 0.0 0 0 [kiblnd_sd_00_00]
>>> 151449 2 2 ffff881ff753edd0 RU 0.0 0 0 [kiblnd_sd_00_01]
>>> 154637 2 29 ffff881f776b1f60 RU 0.0 0 0 [md32_raid6]
>>> 163643 2 11 ffff8820d200bec0 UN 0.0 0 0 [ll_ost_io01_008]
>>> 164083 2 13 ffff8820d2753ec0 UN 0.0 0 0 [ll_ost_io01_034]
>>> 171389 2 5 ffff883fd072de20 UN 0.0 0 0 [ll_ost_io01_058]
>>> 171391 2 17 ffff883fd072ce70 UN 0.0 0 0 [ll_ost_io01_060]
>>> 171399 2 33 ffff883fd9e9ce70 UN 0.0 0 0 [ll_ost_io01_068]
>>> 237019 2 15 ffff882715628fb0 UN 0.0 0 0 [ll_ost_io01_084]
>>> 237033 2 3 ffff881fb0250fb0 UN 0.0 0 0 [ll_ost_io01_098]
>> ...
>>
>> crash> bt 237033
>> PID: 237033 TASK: ffff881fb0250fb0 CPU: 3 COMMAND: "ll_ost_io01_098"
>> #0 [ffff8826fa3e7240] machine_kexec at ffffffff81059bdb
>> #1 [ffff8826fa3e72a0] __crash_kexec at ffffffff811057c2
>> #2 [ffff8826fa3e7370] crash_kexec at ffffffff811058b0
>> #3 [ffff8826fa3e7388] oops_end at ffffffff8168fac8
>> #4 [ffff8826fa3e73b0] die at ffffffff8102e93b
>> #5 [ffff8826fa3e73e0] do_trap at ffffffff8168f180
>> #6 [ffff8826fa3e7430] do_invalid_op at ffffffff8102b144
>> #7 [ffff8826fa3e74e0] invalid_op at ffffffff81698b5e
>> [exception RIP: raid5_get_active_stripe+1809]
>> RIP: ffffffffa0fefd71 RSP: ffff8826fa3e7590 RFLAGS: 00010086
>> RAX: 0000000000000000 RBX: ffff883df051641c RCX: dead000000000200
>> RDX: 0000000000000000 RSI: 0000000000000005 RDI: ffff881e08d54d30
>> RBP: ffff8826fa3e7638 R8: ffff881e08d54d40 R9: 0000000000000080
>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff883df0516400
>> R13: ffff881e08d54d30 R14: 0000000000000000 R15: 0000000000000000
>> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
>> #8 [ffff8826fa3e7640] raid5_make_request at ffffffffa0feff55 [raid456]
>> #9 [ffff8826fa3e7730] md_make_request at ffffffff814f838c
>> #10 [ffff8826fa3e7790] generic_make_request at ffffffff812eedc9
>> #11 [ffff8826fa3e77d8] submit_bio at ffffffff812eef11
>> #12 [ffff8826fa3e7830] osd_submit_bio at ffffffffa10cdbcc [osd_ldiskfs]
>> #13 [ffff8826fa3e7840] osd_do_bio at ffffffffa10d03c1 [osd_ldiskfs]
>> #14 [ffff8826fa3e7960] osd_write_commit at ffffffffa10d0b94 [osd_ldiskfs]
>> #15 [ffff8826fa3e7a00] ofd_commitrw_write at ffffffffa120c734 [ofd]
>> #16 [ffff8826fa3e7a78] ofd_commitrw at ffffffffa120ff07 [ofd]
>> #17 [ffff8826fa3e7b08] obd_commitrw at ffffffffa0c7dc22 [ptlrpc]
>> #18 [ffff8826fa3e7b70] tgt_brw_write at ffffffffa0c55fc1 [ptlrpc]
>> #19 [ffff8826fa3e7cd8] tgt_request_handle at ffffffffa0c52275 [ptlrpc]
>> #20 [ffff8826fa3e7d20] ptlrpc_server_handle_request at ffffffffa0bfe1fb [ptlrpc]
>> #21 [ffff8826fa3e7de8] ptlrpc_main at ffffffffa0c022b0 [ptlrpc]
>> #22 [ffff8826fa3e7ec8] kthread at ffffffff810b0a4f
>> #23 [ffff8826fa3e7f50] ret_from_fork at ffffffff81697218
>>
>>
>> After some disassembly work, I found out that all active tasks are working on the same md (all are raid6):
>>
>> md32’s (struct r5conf *) is 0xffff883df0516400
>>
>> Our crashed task:
>>
>> crash> printf "%s", ((struct r5conf)*0xffff883df0516400).cache_name[0]
>> raid6-md32
>>
>> Example for md32_raid6 task in release_inactive_stripe_list:
>>
>> crash> bt 154637
>> PID: 154637 TASK: ffff881f776b1f60 CPU: 29 COMMAND: "md32_raid6"
>> #0 [ffff883ffc985e48] crash_nmi_callback at ffffffff8104d2e2
>> #1 [ffff883ffc985e58] nmi_handle at ffffffff8168fc77
>> #2 [ffff883ffc985eb0] do_nmi at ffffffff8168fe83
>> #3 [ffff883ffc985ef0] end_repeat_nmi at ffffffff8168f093
>> [exception RIP: _raw_spin_lock_irqsave+64]
>> RIP: ffffffff8168e5f0 RSP: ffff881e8d0cbc60 RFLAGS: 00000006
>> RAX: 00000000000031bb RBX: ffff883df0516740 RCX: 000000000000009a
>> RDX: 0000000000000098 RSI: 000000000000009a RDI: ffff883df051641c
>> RBP: ffff881e8d0cbc60 R8: 0000000000000206 R9: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000007 R12: ffff883df0516400
>> R13: ffff883df051641c R14: 0000000000000006 R15: 0000000000000005
>> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
>> --- <NMI exception stack> ---
>> #4 [ffff881e8d0cbc60] _raw_spin_lock_irqsave at ffffffff8168e5f0
>> #5 [ffff881e8d0cbc68] release_inactive_stripe_list at ffffffffa0fe5500 [raid456]
>> #6 [ffff881e8d0cbcb0] handle_active_stripes at ffffffffa0ff34c2 [raid456]
>> #7 [ffff881e8d0cbd60] raid5d at ffffffffa0ff3c28 [raid456]
>> #8 [ffff881e8d0cbe50] md_thread at ffffffff814fb745
>> #9 [ffff881e8d0cbec8] kthread at ffffffff810b0a4f
>> #10 [ffff881e8d0cbf50] ret_from_fork at ffffffff81697218
>>
>>
>> crash> bt 163643 164083 171389 171391 171399 237019 237033 |grep "exception RIP:"
>> [exception RIP: _raw_spin_lock_irq+63]
>> [exception RIP: _raw_spin_lock_irq+63]
>> [exception RIP: _raw_spin_lock_irq+58]
>> [exception RIP: _raw_spin_lock_irq+63]
>> [exception RIP: _raw_spin_lock_irq+58]
>> [exception RIP: _raw_spin_lock_irq+63]
>> [exception RIP: raid5_get_active_stripe+1809]
>>
>> crash> bt 163643 164083 171389 171391 171399 237019 237033 |grep "raid5_get_active_stripe"
>> #5 [ffff883bcee93588] raid5_get_active_stripe at ffffffffa0fef6cb [raid456]
>> #5 [ffff883ba4af7588] raid5_get_active_stripe at ffffffffa0fef6cb [raid456]
>> #5 [ffff88390877b588] raid5_get_active_stripe at ffffffffa0fef6cb [raid456]
>> #5 [ffff88390803b588] raid5_get_active_stripe at ffffffffa0fef6cb [raid456]
>> #5 [ffff88390831f588] raid5_get_active_stripe at ffffffffa0fef6cb [raid456]
>> #5 [ffff8826fa7f7588] raid5_get_active_stripe at ffffffffa0fef6cb [raid456]
>> [exception RIP: raid5_get_active_stripe+1809]
>>
>> crash> bt 163643 164083 171389 171391 171399 237019 237033 |grep R12
>> R10: 0000000000000003 R11: 0000000000000000 R12: ffff883df0516400
>> R10: 0000000000000001 R11: 0000000000000000 R12: ffff883df0516400
>> R10: 0000000000000005 R11: 0000000000000000 R12: ffff883df0516400
>> R10: 0000000000000007 R11: 0000000000000000 R12: ffff883df0516400
>> R10: 0000000000000009 R11: 0000000000000000 R12: ffff883df0516400
>> R10: 0000000000000009 R11: 0000000000000000 R12: ffff883df0516400
>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff883df0516400
>>
>>
>> The bad stripe_head (sh) is available at (usually in %r13):
>>
>> crash> p ((struct stripe_head)*0xffff881e08d54d30).raid_conf
>> $98 = (struct r5conf *) 0xffff883df0516400
>>
>> and batch_head is not NULL... that's the issue:
>>
>> crash> p ((struct stripe_head)*0xffff881e08d54d30).batch_head
>> $99 = (struct stripe_head *) 0xffff881e08d54d30
>>
>> Full struct dump below. We can see than overwrite_disks is set to 0, state is 0… but this batch_head not set to NULL makes it crash in init_stripe():
>>
>> crash> p ((struct stripe_head)*0xffff881e08d54d30)
>> $6 = {
>> hash = {
>> next = 0x0,
>> pprev = 0x0
>> },
>> lru = {
>> next = 0xffff881e08d54d40,
>> prev = 0xffff881e08d54d40
>> },
>> release_list = {
>> next = 0xffff881dfe405cc0
>> },
>> raid_conf = 0xffff883df0516400,
>> generation = 0,
>> sector = 3701224808,
>> pd_idx = 1,
>> qd_idx = 2,
>> ddf_layout = 0,
>> hash_lock_index = 5,
>> state = 0,
>> count = {
>> counter = 0
>> },
>> bm_seq = 22708787,
>> disks = 10,
>> overwrite_disks = 0,
>> check_state = check_state_idle,
>> reconstruct_state = reconstruct_state_idle,
>> stripe_lock = {
>> {
>> rlock = {
>> raw_lock = {
>> {
>> head_tail = 3709263126,
>> tickets = {
>> head = 56598,
>> tail = 56598
>> }
>> }
>> }
>> }
>> }
>> },
>> cpu = 15,
>> group = 0x0,
>> batch_head = 0xffff881e08d54d30,
>> batch_lock = {
>> {
>> rlock = {
>> raw_lock = {
>> {
>> head_tail = 9961624,
>> tickets = {
>> head = 152,
>> tail = 152
>> }
>> }
>> }
>> }
>> }
>> },
>> batch_list = {
>> next = 0xffff881dfe405d28,
>> prev = 0xffff881e0e2dec98
>> },
>> log_io = 0x0,
>> log_list = {
>> next = 0x0,
>> prev = 0x0
>> },
>> ops = {
>> target = 0,
>> target2 = 0,
>> zero_sum_result = (unknown: 0)
>> },
>> dev = {{
>> req = {
>> bi_sector = 0,
>> bi_next = 0x0,
>> bi_bdev = 0x0,
>> bi_flags = 1,
>> bi_rw = 0,
>> bi_vcnt = 0,
>> bi_idx = 0,
>> bi_phys_segments = 0,
>> bi_size = 0,
>> bi_seg_front_size = 0,
>> bi_seg_back_size = 0,
>> bi_end_io = 0x0,
>> bi_private = 0xffff881e08d54d30,
>> bi_ioc = 0x0,
>> bi_css = 0x0,
>> bi_integrity = 0x0,
>> bi_max_vecs = 1,
>> bi_cnt = {
>> counter = 1
>> },
>> bi_io_vec = 0xffff881e08d54f00,
>> bi_pool = 0x0,
>> {
>> bio_aux = 0x0,
>> __UNIQUE_ID_rh_kabi_hide15 = {
>> rh_reserved1 = 0x0
>> },
>> {<No data fields>}
>> },
>> bi_inline_vecs = 0xffff881e08d54e78
>> },
>> rreq = {
>> bi_sector = 0,
>> bi_next = 0x0,
>> bi_bdev = 0x0,
>> bi_flags = 1,
>> bi_rw = 0,
>> bi_vcnt = 0,
>> bi_idx = 0,
>> bi_phys_segments = 0,
>> bi_size = 0,
>> bi_seg_front_size = 0,
>> bi_seg_back_size = 0,
>> bi_end_io = 0x0,
>> bi_private = 0xffff881e08d54d30,
>> bi_ioc = 0x0,
>> bi_css = 0x0,
>> bi_integrity = 0x0,
>> bi_max_vecs = 1,
>> bi_cnt = {
>> counter = 1
>> },
>> bi_io_vec = 0xffff881e08d54f10,
>> bi_pool = 0x0,
>> {
>> bio_aux = 0x0,
>> __UNIQUE_ID_rh_kabi_hide15 = {
>> rh_reserved1 = 0x0
>> },
>> {<No data fields>}
>> },
>> bi_inline_vecs = 0xffff881e08d54f00
>> },
>> vec = {
>> bv_page = 0xffffea0078236080,
>> bv_len = 4096,
>> bv_offset = 0
>> },
>> rvec = {
>> bv_page = 0x0,
>> bv_len = 0,
>> bv_offset = 0
>> },
>> page = 0xffffea0078236080,
>> orig_page = 0xffffea0078236080,
>> toread = 0x0,
>> read = 0x0,
>> towrite = 0x0,
>> written = 0xffff8824832a7c00,
>> sector = 29609798632,
>> flags = 24,
>
> Seems the flags is R5_OVERWRITE | R5_Insync, handle_stripe_clean_event
> only calls break_stripe_batch_list if do_endio is set to true.
>
> if (head_sh->batch_head && do_endio)
> break_stripe_batch_list(head_sh, STRIPE_EXPAND_SYNC_FLAGS);
>
> And do_endio is set to true if we meet the below condition.
>
> if (!test_bit(R5_LOCKED, &dev->flags) &&
> (test_bit(R5_UPTODATE, &dev->flags) ||
> test_bit(R5_Discard, &dev->flags) ||
> test_bit(R5_SkipCopy, &dev->flags))) {
>
> I guess it is why the batch_head is not null, just my 2 cents.
That’s a very good point, thanks Guoqing!
I checked another similar crash dump, and found out that this same flags was 16 (R5_Insync alone), which doesn’t meet the condition for having do_endio = true neither.
The code below in raid5_end_write_request does directly release a sh->batch_head, couldn’t that be an issue?
static void raid5_end_write_request(struct bio *bi)
{
...
raid5_release_stripe(sh);
if (sh->batch_head && sh != sh->batch_head)
raid5_release_stripe(sh->batch_head);
}
Best,
Stephane
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