[PATCH 5.10 439/545] scsi: zfcp: Fix missing auto port scan and thus missing target ports

Greg Kroah-Hartman
2022-08-19T16:43:22Z

From: Steffen Maier <maier@linux.ibm.com>

commit 4da8c5f76825269f28d6a89fa752934a4bcb6dfa upstream.

Case (1):
The only waiter on wka_port->completion_wq is zfcp_fc_wka_port_get()
trying to open a WKA port. As such it should only be woken up by WKA port
*open* responses, not by WKA port close responses.

Case (2):
A close WKA port response coming in just after having sent a new open WKA
port request and before blocking for the open response with wait_event()
in zfcp_fc_wka_port_get() erroneously renders the wait_event a NOP
because the close handler overwrites wka_port->status. Hence the
wait_event condition is erroneously true and it does not enter blocking
state.

With non-negligible probability, the following time space sequence happens
depending on timing without this fix:

user process ERP thread zfcp work queue tasklet system work queue
============ ========== =============== ======= =================
$ echo 1 > online
zfcp_ccw_set_online
zfcp_ccw_activate
zfcp_erp_adapter_reopen
msleep scan backoff zfcp_erp_strategy
| ...
| zfcp_erp_action_cleanup
| ...
| queue delayed scan_work
| queue ns_up_work
| ns_up_work:
| zfcp_fc_wka_port_get
| open wka request
| open response
| GSPN FC-GS
| RSPN FC-GS [NPIV-only]
| zfcp_fc_wka_port_put
| (--wka->refcount==0)
| sched delayed wka->work
|
~~~Case (1)~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
zfcp_erp_wait
flush scan_work
| wka->work:
| wka->status=CLOSING
| close wka request
| scan_work:
| zfcp_fc_wka_port_get
| (wka->status==CLOSING)
| wka->status=OPENING
| open wka request
| wait_event
| | close response
| | wka->status=OFFLINE
| | wake_up /*WRONG*/
~~~Case (2)~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| wka->work:
| wka->status=CLOSING
| close wka request
zfcp_erp_wait
flush scan_work
| scan_work:
| zfcp_fc_wka_port_get
| (wka->status==CLOSING)
| wka->status=OPENING
| open wka request
| close response
| wka->status=OFFLINE
| wake_up /*WRONG&NOP*/
| wait_event /*NOP*/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| (wka->status!=ONLINE)
| return -EIO
| return early
open response
wka->status=ONLINE
wake_up /*NOP*/

So we erroneously end up with no automatic port scan. This is a big problem
when it happens during boot. The timing is influenced by v3.19 commit
18f87a67e6d6 ("zfcp: auto port scan resiliency").

Fix it by fully mutually excluding zfcp_fc_wka_port_get() and
zfcp_fc_wka_port_offline(). For that to work, we make the latter block
until we got the response for a close WKA port. In order not to penalize
the system workqueue, we move wka_port->work to our own adapter workqueue.
Note that before v2.6.30 commit 828bc1212a68 ("[SCSI] zfcp: Set WKA-port to
offline on adapter deactivation"), zfcp did block in
zfcp_fc_wka_port_offline() as well, but with a different condition.

While at it, make non-functional cleanups to improve code reading in
zfcp_fc_wka_port_get(). If we cannot send the WKA port open request, don't
rely on the subsequent wait_event condition to immediately let this case
pass without blocking. Also don't want to rely on the additional condition
handling the refcount to be skipped just to finally return with -EIO.

Link: https://lore.kernel.org/r/20220729162529.1620730-1-maier@linux.ibm.com
Fixes: 5ab944f97e09 ("[SCSI] zfcp: attach and release SAN nameserver port on demand")
Cc: <stable@vger.kernel.org> #v2.6.28+
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/s390/scsi/zfcp_fc.c | 29 ++++++++++++++++++++---------
drivers/s390/scsi/zfcp_fc.h | 6 ++++--
drivers/s390/scsi/zfcp_fsf.c | 4 ++--
3 files changed, 26 insertions(+), 13 deletions(-)

--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -145,27 +145,33 @@ void zfcp_fc_enqueue_event(struct zfcp_a

static int zfcp_fc_wka_port_get(struct zfcp_fc_wka_port *wka_port)
{
+ int ret = -EIO;
+
if (mutex_lock_interruptible(&wka_port->mutex))
return -ERESTARTSYS;

if (wka_port->status == ZFCP_FC_WKA_PORT_OFFLINE ||
wka_port->status == ZFCP_FC_WKA_PORT_CLOSING) {
wka_port->status = ZFCP_FC_WKA_PORT_OPENING;
- if (zfcp_fsf_open_wka_port(wka_port))
+ if (zfcp_fsf_open_wka_port(wka_port)) {
+ /* could not even send request, nothing to wait for */
wka_port->status = ZFCP_FC_WKA_PORT_OFFLINE;
+ goto out;
+ }
}

- mutex_unlock(&wka_port->mutex);
-
- wait_event(wka_port->completion_wq,
+ wait_event(wka_port->opened,
wka_port->status == ZFCP_FC_WKA_PORT_ONLINE ||
wka_port->status == ZFCP_FC_WKA_PORT_OFFLINE);

if (wka_port->status == ZFCP_FC_WKA_PORT_ONLINE) {
atomic_inc(&wka_port->refcount);
- return 0;
+ ret = 0;
+ goto out;
}
- return -EIO;
+out:
+ mutex_unlock(&wka_port->mutex);
+ return ret;
}

static void zfcp_fc_wka_port_offline(struct work_struct *work)
@@ -181,9 +187,12 @@ static void zfcp_fc_wka_port_offline(str

wka_port->status = ZFCP_FC_WKA_PORT_CLOSING;
if (zfcp_fsf_close_wka_port(wka_port)) {
+ /* could not even send request, nothing to wait for */
wka_port->status = ZFCP_FC_WKA_PORT_OFFLINE;
- wake_up(&wka_port->completion_wq);
+ goto out;
}
+ wait_event(wka_port->closed,
+ wka_port->status == ZFCP_FC_WKA_PORT_OFFLINE);
out:
mutex_unlock(&wka_port->mutex);
}
@@ -193,13 +202,15 @@ static void zfcp_fc_wka_port_put(struct
if (atomic_dec_return(&wka_port->refcount) != 0)
return;
/* wait 10 milliseconds, other reqs might pop in */
- schedule_delayed_work(&wka_port->work, HZ / 100);
+ queue_delayed_work(wka_port->adapter->work_queue, &wka_port->work,
+ msecs_to_jiffies(10));
}

static void zfcp_fc_wka_port_init(struct zfcp_fc_wka_port *wka_port, u32 d_id,
struct zfcp_adapter *adapter)
{
- init_waitqueue_head(&wka_port->completion_wq);
+ init_waitqueue_head(&wka_port->opened);
+ init_waitqueue_head(&wka_port->closed);

wka_port->adapter = adapter;
wka_port->d_id = d_id;
--- a/drivers/s390/scsi/zfcp_fc.h
+++ b/drivers/s390/scsi/zfcp_fc.h
@@ -185,7 +185,8 @@ enum zfcp_fc_wka_status {
/**
* struct zfcp_fc_wka_port - representation of well-known-address (WKA) FC port
* @adapter: Pointer to adapter structure this WKA port belongs to
- * @completion_wq: Wait for completion of open/close command
+ * @opened: Wait for completion of open command
+ * @closed: Wait for completion of close command
* @status: Current status of WKA port
* @refcount: Reference count to keep port open as long as it is in use
* @d_id: FC destination id or well-known-address
@@ -195,7 +196,8 @@ enum zfcp_fc_wka_status {
*/
struct zfcp_fc_wka_port {
struct zfcp_adapter *adapter;
- wait_queue_head_t completion_wq;
+ wait_queue_head_t opened;
+ wait_queue_head_t closed;
enum zfcp_fc_wka_status status;
atomic_t refcount;
u32 d_id;
--- a/drivers/s390/scsi/zfcp_fsf.c
+++ b/drivers/s390/scsi/zfcp_fsf.c
@@ -1889,7 +1889,7 @@ static void zfcp_fsf_open_wka_port_handl
wka_port->status = ZFCP_FC_WKA_PORT_ONLINE;
}
out:
- wake_up(&wka_port->completion_wq);
+ wake_up(&wka_port->opened);
}

/**
@@ -1948,7 +1948,7 @@ static void zfcp_fsf_close_wka_port_hand
}

wka_port->status = ZFCP_FC_WKA_PORT_OFFLINE;
- wake_up(&wka_port->completion_wq);
+ wake_up(&wka_port->closed);
}

/**