Re: [PATCH] iscsi-target: fix hang in iscsit_access_np() when getting tpg->np_login_sem

[Hou Pu <houpu@bytedance.com>]

Hi,

Could anyone help review this patch? It is an important
fix.

Login thread could hang __forever__ and only reboot could
solve this. This happened several times in our production
environment.

np->np_login_timer is shared by all TPGs of a portal.
should be used carefully. If a connection to iqn-TPG A start
login timer, It should not stop by another connection
to iqn-TPG B.

np->np_login_timer protect potential hangs in
__iscsi_target_login_thread.
should be used locally in this function. It should really
not be used in iscsi_target_login_sess_out from workqueue
context.

Thanks,
Hou

On 2020/7/29 9:03 PM, Hou Pu wrote:
> The iscsi target login thread might stuck in following stack:
> 
> cat /proc/`pidof iscsi_np`/stack
> [<0>] down_interruptible+0x42/0x50
> [<0>] iscsit_access_np+0xe3/0x167
> [<0>] iscsi_target_locate_portal+0x695/0x8ac
> [<0>] __iscsi_target_login_thread+0x855/0xb82
> [<0>] iscsi_target_login_thread+0x2f/0x5a
> [<0>] kthread+0xfa/0x130
> [<0>] ret_from_fork+0x1f/0x30
> 
> This could be reproduced by following steps:
> 1. Initiator A try to login iqn1-tpg1 on port 3260. After finishing
>     PDU exchange in the login thread and before the negotiation is
>     finished, at this time the network link is down. In a production
>     environment, this could happen. I could emulated it by bring
>     the network card down in the initiator node by ifconfig eth0 down.
>     (Now A could never finish this login. And tpg->np_login_sem is
>     hold by it).
> 2. Initiator B try to login iqn2-tpg1 on port 3260. After finishing
>     PDU exchange in the login thread. The target expect to process
>     remaining login PDUs in workqueue context.
> 3. Initiator A' try to re-login to iqn1-tpg1 on port 3260 from
>     a new socket. It will wait for tpg->np_login_sem with
>     np->np_login_timer loaded to wait for at most 15 second.
>     (Because the lock is held by A. A never gets a change to
>     release tpg->np_login_sem. so A' should finally get timeout).
> 4. Before A' got timeout. Initiator B gets negotiation failed and
>     calls iscsi_target_login_drop()->iscsi_target_login_sess_out().
>     The np->np_login_timer is canceled. And initiator A' will hang
>     there forever. Because A' is now in the login thread. All other
>     login requests could not be serviced.
> 
> Fix this by moving iscsi_stop_login_thread_timer() out of
> iscsi_target_login_sess_out(). Also remove iscsi_np parameter
> from iscsi_target_login_sess_out().
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Hou Pu <houpu@bytedance.com>
> ---
>   drivers/target/iscsi/iscsi_target_login.c | 6 +++---
>   drivers/target/iscsi/iscsi_target_login.h | 3 +--
>   drivers/target/iscsi/iscsi_target_nego.c  | 3 +--
>   3 files changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/target/iscsi/iscsi_target_login.c b/drivers/target/iscsi/iscsi_target_login.c
> index 85748e338858..893d1b406c29 100644
> --- a/drivers/target/iscsi/iscsi_target_login.c
> +++ b/drivers/target/iscsi/iscsi_target_login.c
> @@ -1149,7 +1149,7 @@ void iscsit_free_conn(struct iscsi_conn *conn)
>   }
>   
>   void iscsi_target_login_sess_out(struct iscsi_conn *conn,
> -		struct iscsi_np *np, bool zero_tsih, bool new_sess)
> +				 bool zero_tsih, bool new_sess)
>   {
>   	if (!new_sess)
>   		goto old_sess_out;
> @@ -1167,7 +1167,6 @@ void iscsi_target_login_sess_out(struct iscsi_conn *conn,
>   	conn->sess = NULL;
>   
>   old_sess_out:
> -	iscsi_stop_login_thread_timer(np);
>   	/*
>   	 * If login negotiation fails check if the Time2Retain timer
>   	 * needs to be restarted.
> @@ -1407,8 +1406,9 @@ static int __iscsi_target_login_thread(struct iscsi_np *np)
>   new_sess_out:
>   	new_sess = true;
>   old_sess_out:
> +	iscsi_stop_login_thread_timer(np);
>   	tpg_np = conn->tpg_np;
> -	iscsi_target_login_sess_out(conn, np, zero_tsih, new_sess);
> +	iscsi_target_login_sess_out(conn, zero_tsih, new_sess);
>   	new_sess = false;
>   
>   	if (tpg) {
> diff --git a/drivers/target/iscsi/iscsi_target_login.h b/drivers/target/iscsi/iscsi_target_login.h
> index 3b8e3639ff5d..fc95e6150253 100644
> --- a/drivers/target/iscsi/iscsi_target_login.h
> +++ b/drivers/target/iscsi/iscsi_target_login.h
> @@ -22,8 +22,7 @@ extern int iscsit_put_login_tx(struct iscsi_conn *, struct iscsi_login *, u32);
>   extern void iscsit_free_conn(struct iscsi_conn *);
>   extern int iscsit_start_kthreads(struct iscsi_conn *);
>   extern void iscsi_post_login_handler(struct iscsi_np *, struct iscsi_conn *, u8);
> -extern void iscsi_target_login_sess_out(struct iscsi_conn *, struct iscsi_np *,
> -				bool, bool);
> +extern void iscsi_target_login_sess_out(struct iscsi_conn *, bool, bool);
>   extern int iscsi_target_login_thread(void *);
>   extern void iscsi_handle_login_thread_timeout(struct timer_list *t);
>   
> diff --git a/drivers/target/iscsi/iscsi_target_nego.c b/drivers/target/iscsi/iscsi_target_nego.c
> index 685d771b51d4..e32d93b92742 100644
> --- a/drivers/target/iscsi/iscsi_target_nego.c
> +++ b/drivers/target/iscsi/iscsi_target_nego.c
> @@ -535,12 +535,11 @@ static bool iscsi_target_sk_check_and_clear(struct iscsi_conn *conn, unsigned in
>   
>   static void iscsi_target_login_drop(struct iscsi_conn *conn, struct iscsi_login *login)
>   {
> -	struct iscsi_np *np = login->np;
>   	bool zero_tsih = login->zero_tsih;
>   
>   	iscsi_remove_failed_auth_entry(conn);
>   	iscsi_target_nego_release(conn);
> -	iscsi_target_login_sess_out(conn, np, zero_tsih, true);
> +	iscsi_target_login_sess_out(conn, zero_tsih, true);
>   }
>   
>   struct conn_timeout {
>