Re: [PATCH v2 11/13] scsi: target: Treat CMD_T_FABRIC_STOP like CMD_T_STOP

[Dmitry Bogdanov <d.bogdanov@yadro.com>]

On Tue, Jan 17, 2023 at 12:45:56PM -0600, Mike Christie wrote:
> 
> On 1/17/23 05:52, Dmitry Bogdanov wrote:
> > On Fri, Jan 13, 2023 at 05:15:12PM +0300, Dmitry Bogdanov wrote:
> >> On Wed, Jan 11, 2023 at 09:08:30PM -0600, Mike Christie wrote:
> >>>
> >>> iscsit will set CMD_T_FABRIC_STOP on running commands when its transport
> >>> connection is down and it can't send/recv IO (tx/rx threads are killed
> >>> or the cleanup thread is run from the one thats up). It will then loop
> >>> over running commands and wait for LIO core to complete them or clean
> >>> them up if they were on an internal queue waiting to be sent or ackd.
> >>>
> >>> Currently, CMD_T_FABRIC_STOP only stops TMRs from operating on the
> >>> command but for isert we need to prevent LIO core from calling into
> >>> iscsit callouts when the connection is being brought down. If LIO core
> >>> queues commands to iscsit and it ends up adding to an internal queue
> >>> instead of passing back to the driver then we can end up hanging waiting
> >>> on command completion that never occurs because it's stuck on the internal
> >>> list (the tx thread is stopped at this time, so it will never loop over
> >>> the response list and call into isert). We also want to sync up on a
> >>> point where we no longer call into isert so it can cleanup it's structs.
> >>>
> >>> This has LIO core treat CMD_T_FABRIC_STOP like CMD_T_STOP during
> >>> command execution and also fixes the locking around the
> >>> target_cmd_interrupted calls so we don't have a case where a command
> >>> is marked CMD_T_COMPLETE and CMD_T_STOP|CMD_T_FABRIC_STOP at the same
> >>> time.
> >>>
> >>> Signed-off-by: Mike Christie <michael.christie@oracle.com>
> >>> ---
> >>>  drivers/target/target_core_sbc.c       |  2 +-
> >>>  drivers/target/target_core_transport.c | 27 +++++++++++++++-----------
> >>>  2 files changed, 17 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
> >>> index 7536ca797606..56136613767f 100644
> >>> --- a/drivers/target/target_core_sbc.c
> >>> +++ b/drivers/target/target_core_sbc.c
> >>> @@ -459,7 +459,7 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
> >>>                  * we don't have to perform the write operation.
> >>>                  */
> >>>                 WARN_ON(!(cmd->transport_state &
> >>> -                       (CMD_T_ABORTED | CMD_T_STOP)));
> >>> +                       (CMD_T_ABORTED | CMD_T_STOP | CMD_T_FABRIC_STOP)));
> >>>                 goto out;
> >>>         }
> >>>         /*
> >>> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> >>> index cb3fdc81ba3b..02a9476945dc 100644
> >>> --- a/drivers/target/target_core_transport.c
> >>> +++ b/drivers/target/target_core_transport.c
> >>> @@ -737,8 +737,8 @@ static int transport_cmd_check_stop_to_fabric(struct se_cmd *cmd)
> >>>          * Determine if frontend context caller is requesting the stopping of
> >>>          * this command for frontend exceptions.
> >>>          */
> >>> -       if (cmd->transport_state & CMD_T_STOP) {
> >>> -               pr_debug("%s:%d CMD_T_STOP for ITT: 0x%08llx\n",
> >>> +       if (cmd->transport_state & (CMD_T_STOP | CMD_T_FABRIC_STOP)) {
> >>> +               pr_debug("%s:%d CMD_T_STOP|CMD_T_FABRIC_STOP for ITT: 0x%08llx\n",
> >>>                         __func__, __LINE__, cmd->tag);
> >>>
> >>>                 spin_unlock_irqrestore(&cmd->t_state_lock, flags);
> >>> @@ -889,7 +889,7 @@ static bool target_cmd_interrupted(struct se_cmd *cmd)
> >>>                 INIT_WORK(&cmd->work, target_abort_work);
> >>>                 queue_work(target_completion_wq, &cmd->work);
> >>>                 return true;
> >>> -       } else if (cmd->transport_state & CMD_T_STOP) {
> >>> +       } else if (cmd->transport_state & (CMD_T_STOP | CMD_T_FABRIC_STOP)) {
> >>>                 if (cmd->transport_complete_callback)
> >>>                         cmd->transport_complete_callback(cmd, false, &post_ret);
> >>>                 complete_all(&cmd->t_transport_stop_comp);
> >>> @@ -907,13 +907,15 @@ void target_complete_cmd_with_sense(struct se_cmd *cmd, u8 scsi_status,
> >>>         int success, cpu;
> >>>         unsigned long flags;
> >>>
> >>> -       if (target_cmd_interrupted(cmd))
> >>> +       spin_lock_irqsave(&cmd->t_state_lock, flags);
> >>
> >> That leads to a hardlock because
> >> target_cmd_interrupted() => cmd->transport_complete_callback() also tooks
> >> cmd->t_state_lock.
> 
> We shouldn't lock up because for the failure cases the transport_complete_callback
> functions don't take the lock. They just cleanup and return.

The second callback (compare_and_write_post) does take the lock always.
Although to be honest, that lock there has no sense.

> > But the taking the lock for read+write of cmd->t*_state is absolutelly right!
> > It would be great if you manage to move transport_complete_callback()
> > into other thread/job.
> 
> I'm not sure why we want to do that since none of the transport_complete_callback
> sleep on failure. It seems to just add more complexity and we only have the 2
> transport_complete_callback uses now, so it seems overkill.

I have a personal interest on that :) Of course, it is just one of the
ways to solve it.

BR,
 Dmitry