Re: [PATCH v2 1/1] scsi: libiscsi: fix NOP race condition

[Lee Duncan]

On 9/25/20 11:41 AM, lduncan@xxxxxxxx wrote:
> From: Lee Duncan <lduncan@xxxxxxxx>
> 
> iSCSI NOPs are sometimes "lost", mistakenly sent to the
> user-land iscsid daemon instead of handled in the kernel,
> as they should be, resulting in a message from the daemon like:
> 
>> iscsid: Got nop in, but kernel supports nop handling.
> 
> This can occur because of the forward- and back-locks
> in the kernel iSCSI code, and the fact that an iSCSI NOP
> response can be processed before processing of the NOP send
> is complete. This can result in "conn->ping_task" being NULL
> in iscsi_nop_out_rsp(), when the pointer is actually in
> the process of being set.
> 
> To work around this, we add a new state to the "ping_task"
> pointer. In addition to NULL (not assigned) and a pointer
> (assigned), we add the state "being set", which is signaled
> with an INVALID pointer (using "-1").
> 
> Signed-off-by: Lee Duncan <lduncan@xxxxxxxx>
> ---
>  drivers/scsi/libiscsi.c | 13 ++++++++++---
>  include/scsi/libiscsi.h |  3 +++
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
> index 1e9c3171fa9f..cade108c33b6 100644
> --- a/drivers/scsi/libiscsi.c
> +++ b/drivers/scsi/libiscsi.c
> @@ -738,6 +738,9 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
>  						   task->conn->session->age);
>  	}
>  
> +	if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK))
> +		WRITE_ONCE(conn->ping_task, task);
> +
>  	if (!ihost->workq) {
>  		if (iscsi_prep_mgmt_task(conn, task))
>  			goto free_task;
> @@ -941,8 +944,11 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
>          struct iscsi_nopout hdr;
>  	struct iscsi_task *task;
>  
> -	if (!rhdr && conn->ping_task)
> -		return -EINVAL;
> +	if (!rhdr) {
> +		if (READ_ONCE(conn->ping_task))
> +			return -EINVAL;
> +		WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK);
> +	}
>  
>  	memset(&hdr, 0, sizeof(struct iscsi_nopout));
>  	hdr.opcode = ISCSI_OP_NOOP_OUT | ISCSI_OP_IMMEDIATE;
> @@ -957,11 +963,12 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
>  
>  	task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0);
>  	if (!task) {
> +		if (!rhdr)
> +			WRITE_ONCE(conn->ping_task, NULL);
>  		iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n");
>  		return -EIO;
>  	} else if (!rhdr) {
>  		/* only track our nops */
> -		conn->ping_task = task;
>  		conn->last_ping = jiffies;
>  	}
>  
> diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h
> index c25fb86ffae9..b3bbd10eb3f0 100644
> --- a/include/scsi/libiscsi.h
> +++ b/include/scsi/libiscsi.h
> @@ -132,6 +132,9 @@ struct iscsi_task {
>  	void			*dd_data;	/* driver/transport data */
>  };
>  
> +/* invalid scsi_task pointer */
> +#define	INVALID_SCSI_TASK	(struct iscsi_task *)-1l
> +
>  static inline int iscsi_task_has_unsol_data(struct iscsi_task *task)
>  {
>  	return task->unsol_r2t.data_length > task->unsol_r2t.sent;
> 

Ping?

-- 
Lee Duncan