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scsi: target: Document when CMD_T_STOP and CMD_T_COMPLETE are set

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Document those aspects of transport_cmd_check_stop_to_fabric() and
transport_generic_free_cmd() of which it is nontrivial to derive these from
their implementation.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Bart Van Assche 2018-06-22 14:52:54 -07:00 committed by Martin K. Petersen
parent 00d909a107
commit 953bcf7ad1
1 changed files with 28 additions and 6 deletions
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34
drivers/target/target_core_transport.c
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@ -632,6 +632,13 @@ static void target_remove_from_state_list(struct se_cmd *cmd)
spin_unlock_irqrestore(&dev->execute_task_lock, flags);
}
/*
* This function is called by the target core after the target core has
* finished processing a SCSI command or SCSI TMF. Both the regular command
* processing code and the code for aborting commands can call this
* function. CMD_T_STOP is set if and only if another thread is waiting
* inside transport_wait_for_tasks() for t_transport_stop_comp.
*/
static int transport_cmd_check_stop_to_fabric(struct se_cmd *cmd)
{
unsigned long flags;
@ -2624,6 +2631,27 @@ static void target_wait_free_cmd(struct se_cmd *cmd, bool *aborted, bool *tas)
spin_unlock_irqrestore(&cmd->t_state_lock, flags);
}
/*
* This function is called by frontend drivers after processing of a command
* has finished.
*
* The protocol for ensuring that either the regular flow or the TMF
* code drops one reference is as follows:
* - Calling .queue_data_in(), .queue_status() or queue_tm_rsp() will cause
* the frontend driver to drop one reference, synchronously or asynchronously.
* - During regular command processing the target core sets CMD_T_COMPLETE
* before invoking one of the .queue_*() functions.
* - The code that aborts commands skips commands and TMFs for which
* CMD_T_COMPLETE has been set.
* - CMD_T_ABORTED is set atomically after the CMD_T_COMPLETE check for
* commands that will be aborted.
* - If the CMD_T_ABORTED flag is set but CMD_T_TAS has not been set
* transport_generic_free_cmd() skips its call to target_put_sess_cmd().
* - For aborted commands for which CMD_T_TAS has been set .queue_status() will
* be called and will drop a reference.
* - For aborted commands for which CMD_T_TAS has not been set .aborted_task()
* will be called. transport_cmd_finish_abort() will drop the final reference.
*/
int transport_generic_free_cmd(struct se_cmd *cmd, int wait_for_tasks)
{
int ret = 0;
@ -2652,12 +2680,6 @@ int transport_generic_free_cmd(struct se_cmd *cmd, int wait_for_tasks)
if (!aborted || tas)
ret = target_put_sess_cmd(cmd);
}
/*
* If the task has been internally aborted due to TMR ABORT_TASK
* or LUN_RESET, target_core_tmr.c is responsible for performing
* the remaining calls to target_put_sess_cmd(), and not the
* callers of this function.
*/
if (aborted) {
pr_debug("Detected CMD_T_ABORTED for ITT: %llu\n", cmd->tag);
wait_for_completion(&cmd->cmd_wait_comp);