Doug reported [1] the following hung task:
INFO: task swapper/0:1 blocked for more than 122 seconds.
Not tainted 5.15.149-21875-gf795ebc40eb8 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:swapper/0 state:D stack: 0 pid: 1 ppid: 0 flags:0x00000008
Call trace:
__switch_to+0xf4/0x1f4
__schedule+0x418/0xb80
schedule+0x5c/0x10c
rpm_resume+0xe0/0x52c
rpm_resume+0x178/0x52c
__pm_runtime_resume+0x58/0x98
clk_pm_runtime_get+0x30/0xb0
clk_disable_unused_subtree+0x58/0x208
clk_disable_unused_subtree+0x38/0x208
clk_disable_unused_subtree+0x38/0x208
clk_disable_unused_subtree+0x38/0x208
clk_disable_unused_subtree+0x38/0x208
clk_disable_unused+0x4c/0xe4
do_one_initcall+0xcc/0x2d8
do_initcall_level+0xa4/0x148
do_initcalls+0x5c/0x9c
do_basic_setup+0x24/0x30
kernel_init_freeable+0xec/0x164
kernel_init+0x28/0x120
ret_from_fork+0x10/0x20
INFO: task kworker/u16:0:9 blocked for more than 122 seconds.
Not tainted 5.15.149-21875-gf795ebc40eb8 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u16:0 state:D stack: 0 pid: 9 ppid: 2 flags:0x00000008
Workqueue: events_unbound deferred_probe_work_func
Call trace:
__switch_to+0xf4/0x1f4
__schedule+0x418/0xb80
schedule+0x5c/0x10c
schedule_preempt_disabled+0x2c/0x48
__mutex_lock+0x238/0x488
__mutex_lock_slowpath+0x1c/0x28
mutex_lock+0x50/0x74
clk_prepare_lock+0x7c/0x9c
clk_core_prepare_lock+0x20/0x44
clk_prepare+0x24/0x30
clk_bulk_prepare+0x40/0xb0
mdss_runtime_resume+0x54/0x1c8
pm_generic_runtime_resume+0x30/0x44
__genpd_runtime_resume+0x68/0x7c
genpd_runtime_resume+0x108/0x1f4
__rpm_callback+0x84/0x144
rpm_callback+0x30/0x88
rpm_resume+0x1f4/0x52c
rpm_resume+0x178/0x52c
__pm_runtime_resume+0x58/0x98
__device_attach+0xe0/0x170
device_initial_probe+0x1c/0x28
bus_probe_device+0x3c/0x9c
device_add+0x644/0x814
mipi_dsi_device_register_full+0xe4/0x170
devm_mipi_dsi_device_register_full+0x28/0x70
ti_sn_bridge_probe+0x1dc/0x2c0
auxiliary_bus_probe+0x4c/0x94
really_probe+0xcc/0x2c8
__driver_probe_device+0xa8/0x130
driver_probe_device+0x48/0x110
__device_attach_driver+0xa4/0xcc
bus_for_each_drv+0x8c/0xd8
__device_attach+0xf8/0x170
device_initial_probe+0x1c/0x28
bus_probe_device+0x3c/0x9c
deferred_probe_work_func+0x9c/0xd8
process_one_work+0x148/0x518
worker_thread+0x138/0x350
kthread+0x138/0x1e0
ret_from_fork+0x10/0x20
The first thread is walking the clk tree and calling
clk_pm_runtime_get() to power on devices required to read the clk
hardware via struct clk_ops::is_enabled(). This thread holds the clk
prepare_lock, and is trying to runtime PM resume a device, when it finds
that the device is in the process of resuming so the thread schedule()s
away waiting for the device to finish resuming before continuing. The
second thread is runtime PM resuming the same device, but the runtime
resume callback is calling clk_prepare(), trying to grab the
prepare_lock waiting on the first thread.
This is a classic ABBA deadlock. To properly fix the deadlock, we must
never runtime PM resume or suspend a device with the clk prepare_lock
held. Actually doing that is near impossible today because the global
prepare_lock would have to be dropped in the middle of the tree, the
device runtime PM resumed/suspended, and then the prepare_lock grabbed
again to ensure consistency of the clk tree topology. If anything
changes with the clk tree in the meantime, we've lost and will need to
start the operation all over again.
Luckily, most of the time we're simply incrementing or decrementing the
runtime PM count on an active device, so we don't have the chance to
schedule away with the prepare_lock held. Let's fix this immediate
problem that can be triggered more easily by simply booting on Qualcomm
sc7180.
Introduce a list of clk_core structures that have been registered, or
are in the process of being registered, that require runtime PM to
operate. Iterate this list and call clk_pm_runtime_get() on each of them
without holding the prepare_lock during clk_disable_unused(). This way
we can be certain that the runtime PM state of the devices will be
active and resumed so we can't schedule away while walking the clk tree
with the prepare_lock held. Similarly, call clk_pm_runtime_put() without
the prepare_lock held to properly drop the runtime PM reference.
Reported-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/20220922084322.RFC.2.I375b6b9e0a0a5348962f004beb3dafee6a12dfbb@changeid/ [1]
Closes: https://issuetracker.google.com/328070191
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Cc: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
Fixes: 9a34b45397e5 ("clk: Add support for runtime PM")
Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxx>
---
drivers/clk/clk.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 92 insertions(+), 2 deletions(-)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index ee80b21f2824..31998ca67b1e 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -37,6 +37,10 @@ static HLIST_HEAD(clk_root_list);
static HLIST_HEAD(clk_orphan_list);
static LIST_HEAD(clk_notifier_list);
+/* List of registered clks that use runtime PM */
+static HLIST_HEAD(clk_rpm_list);
+static DEFINE_MUTEX(clk_rpm_list_lock);
+
static const struct hlist_head *all_lists[] = {
&clk_root_list,
&clk_orphan_list,
@@ -59,6 +63,7 @@ struct clk_core {
struct clk_hw *hw;
struct module *owner;
struct device *dev;
+ struct hlist_node rpm_node;
struct device_node *of_node;
struct clk_core *parent;
struct clk_parent_map *parents;
@@ -122,6 +127,19 @@ static void clk_pm_runtime_put(struct clk_core *core)
pm_runtime_put_sync(core->dev);
}
+static void clk_core_rpm_init(struct clk_core *core)
+{
+ struct device *dev = core->dev;
+
+ if (dev && pm_runtime_enabled(dev)) {
+ core->rpm_enabled = true;
+
+ mutex_lock(&clk_rpm_list_lock);
+ hlist_add_head(&core->rpm_node, &clk_rpm_list);
+ mutex_unlock(&clk_rpm_list_lock);
+ }
+}
+
/*** locking ***/
static void clk_prepare_lock(void)
{
@@ -191,6 +209,63 @@ static void clk_enable_unlock(unsigned long flags)
spin_unlock_irqrestore(&enable_lock, flags);
}
+/*
+ * Call clk_pm_runtime_get() on all runtime PM enabled clks in the clk tree so
+ * that disabling unused clks avoids a deadlock where a device is runtime PM
+ * resuming/suspending and the runtime PM callback is trying to grab the
+ * prepare_lock for something like clk_prepare_enable() while
+ * clk_disable_unused_subtree() holds the prepare_lock and is trying to runtime
+ * PM resume/suspend the device as well.
+ */
+static int clk_pm_runtime_get_all(void)
+{
+ int ret;
+ struct clk_core *core, *failed;
+
+ /*
+ * Grab the list lock to avoid any new clks from being registered
+ * or unregistered.
+ */
+ mutex_lock(&clk_rpm_list_lock);
+
+ /*
+ * Runtime PM "get" all the devices that are needed for the clks
+ * currently registered. Do this without holding the prepare_lock, to
+ * avoid the deadlock.
+ */
+ hlist_for_each_entry(core, &clk_rpm_list, rpm_node) {
+ ret = clk_pm_runtime_get(core);
+ if (ret) {
+ failed = core;
+ pr_err("clk: Failed to runtime PM get '%s' for clk '%s'\n",
+ failed->name, dev_name(failed->dev));
+ goto out;
+ }
+ }
+
+ return 0;
+
+out:
+ hlist_for_each_entry(core, &clk_rpm_list, rpm_node) {
+ if (core == failed)
+ break;
+
+ clk_pm_runtime_put(core);
+ }
+ mutex_unlock(&clk_rpm_list_lock);
+
+ return ret;
+}
+
+static void clk_pm_runtime_put_all(void)
+{
+ struct clk_core *core;
+
+ hlist_for_each_entry(core, &clk_rpm_list, rpm_node)
+ clk_pm_runtime_put(core);
+ mutex_unlock(&clk_rpm_list_lock);
+}
+
static bool clk_core_rate_is_protected(struct clk_core *core)
{
return core->protect_count;
@@ -1431,6 +1506,7 @@ __setup("clk_ignore_unused", clk_ignore_unused_setup);
static int __init clk_disable_unused(void)
{
struct clk_core *core;
+ int ret;
if (clk_ignore_unused) {
pr_warn("clk: Not disabling unused clocks\n");
@@ -1439,6 +1515,13 @@ static int __init clk_disable_unused(void)
pr_info("clk: Disabling unused clocks\n");
+ ret = clk_pm_runtime_get_all();
+ if (ret)
+ return ret;
+ /*
+ * Grab the prepare lock to keep the clk topology stable while iterating
+ * over clks.
+ */
clk_prepare_lock();
hlist_for_each_entry(core, &clk_root_list, child_node)
@@ -1455,6 +1538,8 @@ static int __init clk_disable_unused(void)
clk_prepare_unlock();
+ clk_pm_runtime_put_all();
+
return 0;
}
late_initcall_sync(clk_disable_unused);
@@ -4192,6 +4277,12 @@ static void __clk_release(struct kref *ref)
{
struct clk_core *core = container_of(ref, struct clk_core, ref);
+ if (core->rpm_enabled) {
+ mutex_lock(&clk_rpm_list_lock);
+ hlist_del(&core->rpm_node);
+ mutex_unlock(&clk_rpm_list_lock);
+ }
+
clk_core_free_parent_map(core);
kfree_const(core->name);
kfree(core);
@@ -4231,9 +4322,8 @@ __clk_register(struct device *dev, struct device_node *np, struct clk_hw *hw)
}
core->ops = init->ops;
- if (dev && pm_runtime_enabled(dev))
- core->rpm_enabled = true;
core->dev = dev;
+ clk_core_rpm_init(core);
core->of_node = np;
if (dev && dev->driver)
core->owner = dev->driver->owner;
--
https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git/
https://git.kernel.org/pub/scm/linux/kernel/git/sboyd/spmi.git
