On Wed, Oct 13, 2021 at 12:51:32PM -0500, Mike Christie wrote:
> On 10/13/21 8:21 AM, Konstantin Shelekhin wrote:
> > Hi,
> >
> > I really need the collective wisdom.
> >
> > Not long ago we've uncovered the problem with iSCSI and ABORT TASK
> > handling. Currently it's not possible to abort a WRITE_10 command in
> > TRANSPORT_WRITE_PENDING state, because ABORT TASK will hang itself in
> > the process:
> >
> > # dmesg | tail -2
> > [ 83.563505] ABORT_TASK: Found referenced iSCSI task_tag: 3372979269
> > [ 84.593545] Unable to recover from DataOut timeout while in ERL=0, closing iSCSI connection for I_T Nexus <nexus>
> >
> > # ps aux | awk '$8 ~/D/'
> > root 32 0.0 0.0 0 0 ? D 15:19 0:00 [kworker/0:1+events]
> > root 1187 0.0 0.0 0 0 ? D 15:20 0:00 [iscsi_ttx]
> >
> > # cat /proc/32/stack
> > [<0>] target_put_cmd_and_wait+0x68/0xa0
> > [<0>] core_tmr_abort_task.cold+0x16b/0x192
> > [<0>] target_tmr_work+0x9e/0xe0
> > [<0>] process_one_work+0x1d4/0x370
> > [<0>] worker_thread+0x48/0x3d0
> > [<0>] kthread+0x122/0x140
> > [<0>] ret_from_fork+0x22/0x30
> >
> > # cat /proc/1187/stack
> > [<0>] __transport_wait_for_tasks+0xaf/0x100
> > [<0>] transport_generic_free_cmd+0xe9/0x180
> > [<0>] iscsit_free_cmd+0x50/0xb0
> > [<0>] iscsit_close_connection+0x47d/0x8c0
> > [<0>] iscsit_take_action_for_connection_exit+0x6f/0xf0
> > [<0>] iscsi_target_tx_thread+0x184/0x200
> > [<0>] kthread+0x122/0x140
> > [<0>] ret_from_fork+0x22/0x30
> >
> > What happens:
> >
> > 1. Initiator sends WRITE_10 CDB
> > 2. Target parses the CDB and sends R2T
> > 3. Target starts the Data-Out timer
> > 4. Initiator sends ABORT TASK; no new data from Initiator after this
> > 5. Target starts aborting WRITE_10, gets into core_tmr_abort_task()
> > and starts waiting for the request completion
> > 6. Nothing happens
> > 7. The Data-Out timers expires, connection teardown starts and gets
> > stuck waiting for ABORT TASK that waits for WRITE_10
> >
> > The ABORT TASK processing looks roughly like this:
> >
> > iscsi_rx_opcode
> > iscsi_handle_task_mgt_cmd
> > iscsi_tmr_abort_task
> > transport_generic_handle_tmr
> > if (tmr_cmd->transport_state & CMD_T_ABORTED)
> > target_handle_abort
> > else
> > target_tmr_work
> > if (tmr_cmd->transport_state & CMD_T_ABORTED)
> > target_handle_abort
> > else
> > core_tmr_abort_task
> > ret = __target_check_io_state
> > if (write_cmd->transport_state & CMD_T_STOP)
> > return -1
> > write_cmd->transport_state |= CMD_T_ABORTED
> > return 0
> > if (!ret)
> > list_move_tail(&write_cmd->state_list, &aborted)
> > target_put_cmd_and_wait(&write_cmd)
> >
> > As I see it, the main problem is that the abort path can't initiate the
> > command termination, it simply waits for the request to handle this on
> > the execution path like in target_execute_cmd():
> >
> > target_execute_cmd
> > target_cmd_interrupted
> > INIT_WORK(&cmd->work, target_abort_work)
> >
> > However, in this case the request is not going to be executed because
> > Initiator will not send the Data-Out buffer.
> >
> > I have a couple of ideas on how to fix this, but they all look kinda
> > ugly. The one that currently works around this for me:
> >
> > core_tmr_abort_task():
> >
> > [...]
> >
> > spin_lock_irqsave(&se_cmd->t_state_lock, flags);
> > write_pending = se_cmd->t_state == TRANSPORT_WRITE_PENDING;
> > spin_unlock_irqrestore(&se_cmd->t_state_lock, flags);
> >
> > if (write_pending && se_cmd->se_tfo->abort_write_pending)
> > se_cmd->se_tfo->abort_write_pending(se_cmd);
> >
> > target_put_cmd_and_wait(se_cmd);
> >
> > [...]
> >
> > The new method abort_write_pending() is defined only for iSCSI and calls
> > target_handle_abort(). However, this opens up another can of worms
> > because this code heavily races with R2T sending and requires a couple
> > of checks to "work most of the time". Not ideal, by far.
> >
> > I can make this one better by introducing R2T list draining that ensures
> > the proper order during cleanup, but maybe there is a much easier way
> > that I'm not seeing here.
>
> Ccing Maurizio to make sure I don't add his original bug back.
>
> If I understand you, I think I added this bug in:
>
> commit f36199355c64a39fe82cfddc7623d827c7e050da
> Author: Mike Christie <michael.christie@xxxxxxxxxx>
> Date: Fri Nov 13 19:46:18 2020 -0600
>
> scsi: target: iscsi: Fix cmd abort fabric stop race
>
> With that patch if the abort or a lun reset has got to lio core then we
> are going to be stuck waiting for the data which won't come because we
> killed the iscsi threads.
>
> Can go back to always having the iscsi target clean up the cmd, but if
> LIO has started to abort the cmd we take an extra ref so we don't free
> the cmd from under each other.
>
> This patch is completely untested:
>
>
> diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
> index 2c54c5d8412d..d221e9be7468 100644
> --- a/drivers/target/iscsi/iscsi_target.c
> +++ b/drivers/target/iscsi/iscsi_target.c
> @@ -4090,12 +4090,13 @@ static void iscsit_release_commands_from_conn(struct iscsi_conn *conn)
> spin_lock_irq(&se_cmd->t_state_lock);
> if (se_cmd->transport_state & CMD_T_ABORTED) {
> /*
> - * LIO's abort path owns the cleanup for this,
> - * so put it back on the list and let
> - * aborted_task handle it.
> + * The LIO TMR handler owns the cmd but if
> + * we were waiting for data from the initiator
> + * then we need to internally cleanup to be
> + * able to complete it. Get an extra ref so
> + * we don't free the cmd from under LIO core.
> */
> - list_move_tail(&cmd->i_conn_node,
> - &conn->conn_cmd_list);
> + target_get_sess_cmd(se_cmd, false);
> } else {
> se_cmd->transport_state |= CMD_T_FABRIC_STOP;
> }
The bug was there before. I had to backport this patch in order to
introduce my fix. I can revert it and check what is different, but it's
there in some form.
