Re: [PATCH] libiscsi: Fix iscsi_check_transport_timeouts possible infinite loop

[Mike Christie <michaelc@cs.wisc.edu>]

On 6/30/15, 9:55 AM, Sagi Grimberg wrote:
> From: Ariel Nahum <arieln@mellanox.com>
>
> Connection last_ping is not being updated when iscsi_send_nopout fails.
> Not updating the last_ping will cause firing a timer to a past time
> (last_ping + ping_tmo < current_time) which triggers an infinite loop of
> iscsi_check_transport_timeouts() and hogs the cpu.
>
> Fix this issue by checking the return value of iscsi_send_nopout.
> If it fails set the next_timeout to one second later.
>
> Signed-off-by: Ariel Nahum <arieln@mellanox.com>
> Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
> ---
>   drivers/scsi/libiscsi.c |   15 ++++++++++-----
>   1 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
> index 8053f24..1ea4213 100644
> --- a/drivers/scsi/libiscsi.c
> +++ b/drivers/scsi/libiscsi.c
> @@ -979,13 +979,13 @@ static void iscsi_tmf_rsp(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
>   	wake_up(&conn->ehwait);
>   }
>
> -static void iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
> +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;
> +		return -EINVAL;
>
>   	memset(&hdr, 0, sizeof(struct iscsi_nopout));
>   	hdr.opcode = ISCSI_OP_NOOP_OUT | ISCSI_OP_IMMEDIATE;
> @@ -999,13 +999,16 @@ static void iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
>   		hdr.ttt = RESERVED_ITT;
>
>   	task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0);
> -	if (!task)
> +	if (!task) {


Are you hitting the failure case in the first chunk of the patch or the 
failure right above? If the latter, why is it failing?

>   		iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n");
> +		return -EIO;
> +	}
>   	else if (!rhdr) {

I think the coding style is wrong. It should be:

if () {

} else if {

}

>   		/* only track our nops */
>   		conn->ping_task = task;
>   		conn->last_ping = jiffies;
>   	}
> +	return 0;
>   }
>
>   static int iscsi_nop_out_rsp(struct iscsi_task *task,
> @@ -2095,8 +2098,10 @@ static void iscsi_check_transport_timeouts(unsigned long data)
>   	if (time_before_eq(last_recv + recv_timeout, jiffies)) {
>   		/* send a ping to try to provoke some traffic */
>   		ISCSI_DBG_CONN(conn, "Sending nopout as ping\n");
> -		iscsi_send_nopout(conn, NULL);
> -		next_timeout = conn->last_ping + (conn->ping_timeout * HZ);
> +		if (iscsi_send_nopout(conn, NULL))
> +			next_timeout = jiffies + (1 * HZ);
> +		else
> +			next_timeout = conn->last_ping + (conn->ping_timeout * HZ);
>   	} else
>   		next_timeout = last_recv + recv_timeout;
>
>
n