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

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

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.
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.

> > +       if (target_cmd_interrupted(cmd)) {
> > +               spin_unlock_irqrestore(&cmd->t_state_lock, flags);
> >                 return;
> > +       }
> > 
> >         cmd->scsi_status = scsi_status;
> >         cmd->sense_reason = sense_reason;
> > 
> > -       spin_lock_irqsave(&cmd->t_state_lock, flags);
> >         switch (cmd->scsi_status) {
> >         case SAM_STAT_CHECK_CONDITION:
> >                 if (cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE)