[PATCH 1/6] media: az6007: fix CAM status polling after disconnect

[Josef Schlehofer <pepe.schlehofer@gmail.com>]

az6007_ci_poll_slot_status() returns -EIO when the status request fails.
dvb_ca_en50221 treats the return value as a bitmask, so -EIO is
interpreted as CAM_PRESENT|CAM_CHANGED. The CA state machine then
handles a CAM change for every failed poll, without sleeping in between.

After an unplug, every poll fails this way and the CA thread can spin
forever in dvb_ca_en50221_thread_state_machine(), preventing the USB
disconnect from completing. This happened when unplugging a TechniSat
CableStar Combo HD CI with a CAM inserted, and rcu_sched reported a
stall.

Report no CAM when the status request or buffer allocation fails, and
only inspect the status byte when the request returned data. A read
error while a CAM is present is then treated as a removal and the CAM is
reinitialised after the next successful poll.

Fixes: 962f8f67e486 ("[media] Add CI support to az6007 driver")
Cc: stable@vger.kernel.org
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
---
 drivers/media/usb/dvb-usb-v2/az6007.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/media/usb/dvb-usb-v2/az6007.c b/drivers/media/usb/dvb-usb-v2/az6007.c
index 65ef045b74ca..4ce1afe01c3b 100644
--- a/drivers/media/usb/dvb-usb-v2/az6007.c
+++ b/drivers/media/usb/dvb-usb-v2/az6007.c
@@ -526,7 +526,7 @@ static int az6007_ci_poll_slot_status(struct dvb_ca_en50221 *ca, int slot, int o
 
 	b = kmalloc(12, GFP_KERNEL);
 	if (!b)
-		return -ENOMEM;
+		return 0;
 	mutex_lock(&state->ca_mutex);
 
 	req = 0xC5;
@@ -535,16 +535,18 @@ static int az6007_ci_poll_slot_status(struct dvb_ca_en50221 *ca, int slot, int o
 	blen = 1;
 
 	ret = az6007_read(d, req, value, index, b, blen);
-	if (ret < 0) {
+	if (ret < 0)
 		pr_warn("usb in operation failed. (%d)\n", ret);
-		ret = -EIO;
-	} else
-		ret = 0;
 
-	if (!ret && b[0] == 1) {
+	/*
+	 * The return value is a mask of DVB_CA_EN50221_POLL_* flags, not an
+	 * error code, so report no CAM when the status cannot be read.
+	 */
+	if (ret > 0 && b[0] == 1)
 		ret = DVB_CA_EN50221_POLL_CAM_PRESENT |
 		      DVB_CA_EN50221_POLL_CAM_READY;
-	}
+	else
+		ret = 0;
 
 	mutex_unlock(&state->ca_mutex);
 	kfree(b);
-- 
2.54.0 (Apple Git-157)