Re: [PATCH v2] scsi:libiscsi: Hold back_lock when calling iscsi_complete_task

[Lee Duncan]

On 3/6/19 10:23 AM, Chris Leech wrote:
> On Mon, Feb 25, 2019 at 09:41:30AM -0800, Lee Duncan wrote:
>> From: Lee Duncan <lduncan@xxxxxxxx>
>>
>> If there is an error queueing an iscsi command in
>> iscsi_queuecommand(), for example if the transport fails
>> to take the command in sessuin->tt->xmit_task(), then
>> the error path can call iscsi_complete_task() without
>> first aquiring the back_lock as required. This can
>> lead to things like ITT pool can get corrupt, resulting
>> in duplicate ITTs being sent out.
>>
>> The solution is to hold the back_lock around
>> iscsi_complete_task() calls, and to add a little commenting
>> to help others understand when back_lock must be held.
>>
>> Signed-off-by: Lee Duncan <lduncan@xxxxxxxx>
>> ---
> 
> Lee,
> 
> Quick question, can you confirm that you tested this with lockdep?
> 
> It seems right to me, it's just that we've been hit with lockdep
> problems dealing with these locks before.
> 
> - Chris

I'm glad you asked, to keep me honest -- I had not done it yet, because
it seemed obvious to me.

But I did check today, and did not find any deadlock nor leaks. I was
testing on a 5.0.0-1 kernel.

> 
>>  drivers/scsi/libiscsi.c | 22 ++++++++++++++++++++--
>>  1 file changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
>> index b8d325ce8754..ef7871e8c6bd 100644
>> --- a/drivers/scsi/libiscsi.c
>> +++ b/drivers/scsi/libiscsi.c
>> @@ -838,7 +838,7 @@ EXPORT_SYMBOL_GPL(iscsi_conn_send_pdu);
>>   * @datalen: len of buffer
>>   *
>>   * iscsi_cmd_rsp sets up the scsi_cmnd fields based on the PDU and
>> - * then completes the command and task.
>> + * then completes the command and task. called under back_lock
>>   **/
>>  static void iscsi_scsi_cmd_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
>>  			       struct iscsi_task *task, char *data,
>> @@ -941,6 +941,9 @@ static void iscsi_scsi_cmd_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
>>   * @conn: iscsi connection
>>   * @hdr:  iscsi pdu
>>   * @task: scsi command task
>> + *
>> + * iscsi_data_in_rsp sets up the scsi_cmnd fields based on the data received
>> + * then completes the command and task. called under back_lock
>>   **/
>>  static void
>>  iscsi_data_in_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
>> @@ -1025,6 +1028,16 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
>>  	return 0;
>>  }
>>  
>> +/**
>> + * iscsi_nop_out_rsp - SCSI NOP Response processing
>> + * @task: scsi command task
>> + * @nop: the nop structure
>> + * @data: where to put the data
>> + * @datalen: length of data
>> + *
>> + * iscsi_nop_out_rsp handles nop response from use or
>> + * from user space. called under back_lock
>> + **/
>>  static int iscsi_nop_out_rsp(struct iscsi_task *task,
>>  			     struct iscsi_nopin *nop, char *data, int datalen)
>>  {
>> @@ -1791,7 +1804,9 @@ int iscsi_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *sc)
>>  	return 0;
>>  
>>  prepd_reject:
>> +	spin_lock_bh(&session->back_lock);
>>  	iscsi_complete_task(task, ISCSI_TASK_REQUEUE_SCSIQ);
>> +	spin_unlock_bh(&session->back_lock);
>>  reject:
>>  	spin_unlock_bh(&session->frwd_lock);
>>  	ISCSI_DBG_SESSION(session, "cmd 0x%x rejected (%d)\n",
>> @@ -1799,7 +1814,9 @@ int iscsi_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *sc)
>>  	return SCSI_MLQUEUE_TARGET_BUSY;
>>  
>>  prepd_fault:
>> +	spin_lock_bh(&session->back_lock);
>>  	iscsi_complete_task(task, ISCSI_TASK_REQUEUE_SCSIQ);
>> +	spin_unlock_bh(&session->back_lock);
>>  fault:
>>  	spin_unlock_bh(&session->frwd_lock);
>>  	ISCSI_DBG_SESSION(session, "iscsi: cmd 0x%x is not queued (%d)\n",
>> @@ -3121,8 +3138,9 @@ fail_mgmt_tasks(struct iscsi_session *session, struct iscsi_conn *conn)
>>  		state = ISCSI_TASK_ABRT_SESS_RECOV;
>>  		if (task->state == ISCSI_TASK_PENDING)
>>  			state = ISCSI_TASK_COMPLETED;
>> +		spin_lock_bh(&session->back_lock);
>>  		iscsi_complete_task(task, state);
>> -
>> +		spin_unlock_bh(&session->back_lock);
>>  	}
>>  }
>>  
>> -- 
>> 2.16.4
>>
>