[PATCH 5.10 040/103] s390/qeth: fix deadlock during recovery

Greg Kroah-Hartman
2021-01-15T12:48:15Z

From: Julian Wiedmann <jwi@linux.ibm.com>

[ Upstream commit 0b9902c1fcc59ba75268386c0420a554f8844168 ]

When qeth_dev_layer2_store() - holding the discipline_mutex - waits
inside qeth_l*_remove_device() for a qeth_do_reset() thread to complete,
we can hit a deadlock if qeth_do_reset() concurrently calls
qeth_set_online() and thus tries to aquire the discipline_mutex.

Move the discipline_mutex locking outside of qeth_set_online() and
qeth_set_offline(), and turn the discipline into a parameter so that
callers understand the dependency.

To fix the deadlock, we can now relax the locking:
As already established, qeth_l*_remove_device() waits for
qeth_do_reset() to complete. So qeth_do_reset() itself is under no risk
of having card->discipline ripped out while it's running, and thus
doesn't need to take the discipline_mutex.

Fixes: 9dc48ccc68b9 ("qeth: serialize sysfs-triggered device configurations")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/s390/net/qeth_core.h | 3 ++-
drivers/s390/net/qeth_core_main.c | 35 ++++++++++++++++++++++-------------
drivers/s390/net/qeth_l2_main.c | 7 +++++--
drivers/s390/net/qeth_l3_main.c | 7 +++++--
4 files changed, 34 insertions(+), 18 deletions(-)

--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -1075,7 +1075,8 @@ struct qeth_card *qeth_get_card_by_busid
void qeth_set_allowed_threads(struct qeth_card *card, unsigned long threads,
int clear_start_mask);
int qeth_threads_running(struct qeth_card *, unsigned long);
-int qeth_set_offline(struct qeth_card *card, bool resetting);
+int qeth_set_offline(struct qeth_card *card, const struct qeth_discipline *disc,
+ bool resetting);

int qeth_send_ipa_cmd(struct qeth_card *, struct qeth_cmd_buffer *,
int (*reply_cb)
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -5300,12 +5300,12 @@ out:
return rc;
}

-static int qeth_set_online(struct qeth_card *card)
+static int qeth_set_online(struct qeth_card *card,
+ const struct qeth_discipline *disc)
{
bool carrier_ok;
int rc;

- mutex_lock(&card->discipline_mutex);
mutex_lock(&card->conf_mutex);
QETH_CARD_TEXT(card, 2, "setonlin");

@@ -5322,7 +5322,7 @@ static int qeth_set_online(struct qeth_c
/* no need for locking / error handling at this early stage: */
qeth_set_real_num_tx_queues(card, qeth_tx_actual_queues(card));

- rc = card->discipline->set_online(card, carrier_ok);
+ rc = disc->set_online(card, carrier_ok);
if (rc)
goto err_online;

@@ -5330,7 +5330,6 @@ static int qeth_set_online(struct qeth_c
kobject_uevent(&card->gdev->dev.kobj, KOBJ_CHANGE);

mutex_unlock(&card->conf_mutex);
- mutex_unlock(&card->discipline_mutex);
return 0;

err_online:
@@ -5345,15 +5344,14 @@ err_hardsetup:
qdio_free(CARD_DDEV(card));

mutex_unlock(&card->conf_mutex);
- mutex_unlock(&card->discipline_mutex);
return rc;
}

-int qeth_set_offline(struct qeth_card *card, bool resetting)
+int qeth_set_offline(struct qeth_card *card, const struct qeth_discipline *disc,
+ bool resetting)
{
int rc, rc2, rc3;

- mutex_lock(&card->discipline_mutex);
mutex_lock(&card->conf_mutex);
QETH_CARD_TEXT(card, 3, "setoffl");

@@ -5374,7 +5372,7 @@ int qeth_set_offline(struct qeth_card *c

cancel_work_sync(&card->rx_mode_work);

- card->discipline->set_offline(card);
+ disc->set_offline(card);

qeth_qdio_clear_card(card, 0);
qeth_drain_output_queues(card);
@@ -5395,16 +5393,19 @@ int qeth_set_offline(struct qeth_card *c
kobject_uevent(&card->gdev->dev.kobj, KOBJ_CHANGE);

mutex_unlock(&card->conf_mutex);
- mutex_unlock(&card->discipline_mutex);
return 0;
}
EXPORT_SYMBOL_GPL(qeth_set_offline);

static int qeth_do_reset(void *data)
{
+ const struct qeth_discipline *disc;
struct qeth_card *card = data;
int rc;

+ /* Lock-free, other users will block until we are done. */
+ disc = card->discipline;
+
QETH_CARD_TEXT(card, 2, "recover1");
if (!qeth_do_run_thread(card, QETH_RECOVER_THREAD))
return 0;
@@ -5412,8 +5413,8 @@ static int qeth_do_reset(void *data)
dev_warn(&card->gdev->dev,
"A recovery process has been started for the device\n");

- qeth_set_offline(card, true);
- rc = qeth_set_online(card);
+ qeth_set_offline(card, disc, true);
+ rc = qeth_set_online(card, disc);
if (!rc) {
dev_info(&card->gdev->dev,
"Device successfully recovered!\n");
@@ -6423,7 +6424,10 @@ static int qeth_core_set_online(struct c
}
}

- rc = qeth_set_online(card);
+ mutex_lock(&card->discipline_mutex);
+ rc = qeth_set_online(card, card->discipline);
+ mutex_unlock(&card->discipline_mutex);
+
err:
return rc;
}
@@ -6431,8 +6435,13 @@ err:
static int qeth_core_set_offline(struct ccwgroup_device *gdev)
{
struct qeth_card *card = dev_get_drvdata(&gdev->dev);
+ int rc;

- return qeth_set_offline(card, false);
+ mutex_lock(&card->discipline_mutex);
+ rc = qeth_set_offline(card, card->discipline, false);
+ mutex_unlock(&card->discipline_mutex);
+
+ return rc;
}

static void qeth_core_shutdown(struct ccwgroup_device *gdev)
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -2207,8 +2207,11 @@ static void qeth_l2_remove_device(struct
qeth_set_allowed_threads(card, 0, 1);
wait_event(card->wait_q, qeth_threads_running(card, 0xffffffff) == 0);

- if (gdev->state == CCWGROUP_ONLINE)
- qeth_set_offline(card, false);
+ if (gdev->state == CCWGROUP_ONLINE) {
+ mutex_lock(&card->discipline_mutex);
+ qeth_set_offline(card, card->discipline, false);
+ mutex_unlock(&card->discipline_mutex);
+ }

cancel_work_sync(&card->close_dev_work);
if (card->dev->reg_state == NETREG_REGISTERED)
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -1973,8 +1973,11 @@ static void qeth_l3_remove_device(struct
qeth_set_allowed_threads(card, 0, 1);
wait_event(card->wait_q, qeth_threads_running(card, 0xffffffff) == 0);

- if (cgdev->state == CCWGROUP_ONLINE)
- qeth_set_offline(card, false);
+ if (cgdev->state == CCWGROUP_ONLINE) {
+ mutex_lock(&card->discipline_mutex);
+ qeth_set_offline(card, card->discipline, false);
+ mutex_unlock(&card->discipline_mutex);
+ }

cancel_work_sync(&card->close_dev_work);
if (card->dev->reg_state == NETREG_REGISTERED)