Re: iscsi_trx going into D state

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Hello Robert, Zhu & Co,

Thanks for your detailed bug report.  Comments inline below.

On Mon, 2016-10-17 at 22:42 -0600, Robert LeBlanc wrote:
> Sorry I forget that Android has an aversion to plain text emails.
> 
> If we can provide any information to help, let us know. We are willing
> to patch in more debug statements or whatever you think might help.
> Today has been a difficult day. Thanks for looking into it, I tried
> looking at it, but it is way over my head.
> 
> ----------------
> Robert LeBlanc
> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1
> 
> 
> On Mon, Oct 17, 2016 at 9:06 PM, Zhu Lingshan <lszhu@xxxxxxxx> wrote:
> > Hi Robert,
> >
> > I think the reason why you can not logout the targets is that iscsi_np in D
> > status. I think the patches fixed something, but it seems to be more than
> > one code path can trigger these similar issues. as you can see, there are
> > several call stacks, I am still working on it. Actually in my environment I
> > see there is another call stack not listed in your mail....
> >
> > Thanks,
> > BR
> > Zhu Lingshan
> >
> >
> > On 10/18/2016 03:11 AM, Robert LeBlanc wrote:
> >>
> >> Sorry hit send too soon.
> >>
> >> In addition, on the client we see:
> >> # ps -aux | grep D | grep kworker
> >> root      5583  0.0  0.0      0     0 ?        D    11:55   0:03
> >> [kworker/11:0]
> >> root      7721  0.1  0.0      0     0 ?        D    12:00   0:04
> >> [kworker/4:25]
> >> root     10877  0.0  0.0      0     0 ?        D    09:27   0:00
> >> [kworker/22:1]
> >> root     11246  0.0  0.0      0     0 ?        D    10:28   0:00
> >> [kworker/30:2]
> >> root     14034  0.0  0.0      0     0 ?        D    12:20   0:02
> >> [kworker/19:15]
> >> root     14048  0.0  0.0      0     0 ?        D    12:20   0:00
> >> [kworker/16:0]
> >> root     15871  0.0  0.0      0     0 ?        D    12:25   0:00
> >> [kworker/13:0]
> >> root     17442  0.0  0.0      0     0 ?        D    12:28   0:00
> >> [kworker/9:1]
> >> root     17816  0.0  0.0      0     0 ?        D    12:30   0:00
> >> [kworker/11:1]
> >> root     18744  0.0  0.0      0     0 ?        D    12:32   0:00
> >> [kworker/10:2]
> >> root     19060  0.0  0.0      0     0 ?        D    12:32   0:00
> >> [kworker/29:0]
> >> root     21748  0.0  0.0      0     0 ?        D    12:40   0:00
> >> [kworker/21:0]
> >> root     21967  0.0  0.0      0     0 ?        D    12:40   0:00
> >> [kworker/22:0]
> >> root     21978  0.0  0.0      0     0 ?        D    12:40   0:00
> >> [kworker/22:2]
> >> root     22024  0.0  0.0      0     0 ?        D    12:40   0:00
> >> [kworker/22:4]
> >> root     22035  0.0  0.0      0     0 ?        D    12:40   0:00
> >> [kworker/22:5]
> >> root     22060  0.0  0.0      0     0 ?        D    12:40   0:00
> >> [kworker/16:1]
> >> root     22282  0.0  0.0      0     0 ?        D    12:41   0:00
> >> [kworker/26:0]
> >> root     22362  0.0  0.0      0     0 ?        D    12:42   0:00
> >> [kworker/18:9]
> >> root     22426  0.0  0.0      0     0 ?        D    12:42   0:00
> >> [kworker/16:3]
> >> root     23298  0.0  0.0      0     0 ?        D    12:43   0:00
> >> [kworker/12:1]
> >> root     23302  0.0  0.0      0     0 ?        D    12:43   0:00
> >> [kworker/12:5]
> >> root     24264  0.0  0.0      0     0 ?        D    12:46   0:00
> >> [kworker/30:1]
> >> root     24271  0.0  0.0      0     0 ?        D    12:46   0:00
> >> [kworker/14:8]
> >> root     24441  0.0  0.0      0     0 ?        D    12:47   0:00
> >> [kworker/9:7]
> >> root     24443  0.0  0.0      0     0 ?        D    12:47   0:00
> >> [kworker/9:9]
> >> root     25005  0.0  0.0      0     0 ?        D    12:48   0:00
> >> [kworker/30:3]
> >> root     25158  0.0  0.0      0     0 ?        D    12:49   0:00
> >> [kworker/9:12]
> >> root     26382  0.0  0.0      0     0 ?        D    12:52   0:00
> >> [kworker/13:2]
> >> root     26453  0.0  0.0      0     0 ?        D    12:52   0:00
> >> [kworker/21:2]
> >> root     26724  0.0  0.0      0     0 ?        D    12:53   0:00
> >> [kworker/19:1]
> >> root     28400  0.0  0.0      0     0 ?        D    05:20   0:00
> >> [kworker/25:1]
> >> root     29552  0.0  0.0      0     0 ?        D    11:40   0:00
> >> [kworker/17:1]
> >> root     29811  0.0  0.0      0     0 ?        D    11:40   0:00
> >> [kworker/7:10]
> >> root     31903  0.0  0.0      0     0 ?        D    11:43   0:00
> >> [kworker/26:1]
> >>
> >> And all of the processes have this stack:
> >> [<ffffffffa0727ed5>] iser_release_work+0x25/0x60 [ib_iser]
> >> [<ffffffff8109633f>] process_one_work+0x14f/0x400
> >> [<ffffffff81096bb4>] worker_thread+0x114/0x470
> >> [<ffffffff8109c6f8>] kthread+0xd8/0xf0
> >> [<ffffffff8172004f>] ret_from_fork+0x3f/0x70
> >> [<ffffffffffffffff>] 0xffffffffffffffff
> >>
> >> We are not able to log out of the sessions in all cases. And have to
> >> restart the box.
> >>
> >> iscsiadm -m session will show messages like:
> >> iscsiadm: could not read session targetname: 5
> >> iscsiadm: could not find session info for session100
> >> iscsiadm: could not read session targetname: 5
> >> iscsiadm: could not find session info for session101
> >> iscsiadm: could not read session targetname: 5
> >> iscsiadm: could not find session info for session103
> >> ...
> >>
> >> I can't find any way to force iscsiadm to clean up these sessions
> >> possibly due to tasks in D state.
> >> ----------------
> >> Robert LeBlanc
> >> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1
> >>
> >>
> >> On Mon, Oct 17, 2016 at 10:32 AM, Robert LeBlanc <robert@xxxxxxxxxxxxx>
> >> wrote:
> >>>
> >>> Some more info as we hit this this morning. We have volumes mirrored
> >>> between two targets and we had one target on the kernel with the three
> >>> patches mentioned in this thread [0][1][2] and the other was on a
> >>> kernel without the patches. We decided that after a week and a half we
> >>> wanted to get both targets on the same kernel so we rebooted the
> >>> non-patched target. Within an hour we saw iSCSI in D state with the
> >>> same stack trace so it seems that we are not hitting any of the
> >>> WARN_ON lines. We are getting both iscsi_trx and iscsi_np both in D
> >>> state, this time we have two iscsi_trx processes in D state. I don't
> >>> know if stale sessions on the clients could be contributing to this
> >>> issue (the target trying to close non-existent sessions??). This is on
> >>> 4.4.23. Any more debug info we can throw at this problem to help?
> >>>
> >>> Thank you,
> >>> Robert LeBlanc
> >>>
> >>> # ps aux | grep D | grep iscsi
> >>> root     16525  0.0  0.0      0     0 ?        D    08:50   0:00
> >>> [iscsi_np]
> >>> root     16614  0.0  0.0      0     0 ?        D    08:50   0:00
> >>> [iscsi_trx]
> >>> root     16674  0.0  0.0      0     0 ?        D    08:50   0:00
> >>> [iscsi_trx]
> >>>
> >>> # for i in 16525 16614 16674; do echo $i; cat /proc/$i/stack; done
> >>> 16525
> >>> [<ffffffff814f0d5f>] iscsit_stop_session+0x19f/0x1d0
> >>> [<ffffffff814e2516>] iscsi_check_for_session_reinstatement+0x1e6/0x270
> >>> [<ffffffff814e4ed0>] iscsi_target_check_for_existing_instances+0x30/0x40
> >>> [<ffffffff814e5020>] iscsi_target_do_login+0x140/0x640
> >>> [<ffffffff814e63bc>] iscsi_target_start_negotiation+0x1c/0xb0
> >>> [<ffffffff814e410b>] iscsi_target_login_thread+0xa9b/0xfc0
> >>> [<ffffffff8109c748>] kthread+0xd8/0xf0
> >>> [<ffffffff8172018f>] ret_from_fork+0x3f/0x70
> >>> [<ffffffffffffffff>] 0xffffffffffffffff
> >>> 16614
> >>> [<ffffffff814cca79>] target_wait_for_sess_cmds+0x49/0x1a0
> >>> [<ffffffffa064692b>] isert_wait_conn+0x1ab/0x2f0 [ib_isert]
> >>> [<ffffffff814f0ef2>] iscsit_close_connection+0x162/0x870
> >>> [<ffffffff814df9bf>] iscsit_take_action_for_connection_exit+0x7f/0x100
> >>> [<ffffffff814f00a0>] iscsi_target_rx_thread+0x5a0/0xe80
> >>> [<ffffffff8109c748>] kthread+0xd8/0xf0
> >>> [<ffffffff8172018f>] ret_from_fork+0x3f/0x70
> >>> [<ffffffffffffffff>] 0xffffffffffffffff
> >>> 16674
> >>> [<ffffffff814cca79>] target_wait_for_sess_cmds+0x49/0x1a0
> >>> [<ffffffffa064692b>] isert_wait_conn+0x1ab/0x2f0 [ib_isert]
> >>> [<ffffffff814f0ef2>] iscsit_close_connection+0x162/0x870
> >>> [<ffffffff814df9bf>] iscsit_take_action_for_connection_exit+0x7f/0x100
> >>> [<ffffffff814f00a0>] iscsi_target_rx_thread+0x5a0/0xe80
> >>> [<ffffffff8109c748>] kthread+0xd8/0xf0
> >>> [<ffffffff8172018f>] ret_from_fork+0x3f/0x70
> >>> [<ffffffffffffffff>] 0xffffffffffffffff
> >>>
> >>>
> >>> [0] https://www.spinics.net/lists/target-devel/msg13463.html
> >>> [1] http://marc.info/?l=linux-scsi&m=147282568910535&w=2
> >>> [2] http://www.spinics.net/lists/linux-scsi/msg100221.html

The call chain above is iscsi session reinstatement driven by
open-iscsi/iser resulting in target-core to sleep indefinitely, waiting
for outstanding target-core backend driver se_cmd I/O to complete in
order to make forward progress.

Note, there is a v4.1+ se_cmd->cmd_kref reference leak bug for
TMR ABORT_TASK during simultaneous target back-end I/O completion
timeouts here:

http://www.spinics.net/lists/target-devel/msg13530.html

If you are actively observing TMR ABORT_TASK preceding the hung task
timeout warnings above with v4.4.y + v4.2.y iser-target exports, then
it's likely the same bug.  Please apply the patch on your v4.x setup to
verify.

If no TMR ABORT_TASK timeouts + session reinstatements are occurring on
your iser-target setup, then it is a separate bug.

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