6.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stephen Boyd sboyd@kernel.org
[ Upstream commit e581cf5d216289ef292d1a4036d53ce90e122469 ]
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. We remove the calls to clk_pm_runtime_{get,put}() in this path because they're superfluous now that we know the devices are runtime resumed.
Reported-by: Douglas Anderson dianders@chromium.org Closes: https://lore.kernel.org/all/20220922084322.RFC.2.I375b6b9e0a0a5348962f004beb... [1] Closes: https://issuetracker.google.com/328070191 Cc: Marek Szyprowski m.szyprowski@samsung.com Cc: Ulf Hansson ulf.hansson@linaro.org Cc: Krzysztof Kozlowski krzk@kernel.org Fixes: 9a34b45397e5 ("clk: Add support for runtime PM") Signed-off-by: Stephen Boyd sboyd@kernel.org Link: https://lore.kernel.org/r/20240325184204.745706-5-sboyd@kernel.org Reviewed-by: Douglas Anderson dianders@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/clk/clk.c | 117 +++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 105 insertions(+), 12 deletions(-)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index d5a1e68ee20b7..7162b45da91f8 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 +127,89 @@ static void clk_pm_runtime_put(struct clk_core *core) pm_runtime_put_sync(core->dev); }
+/** + * clk_pm_runtime_get_all() - Runtime "get" all clk provider devices + * + * 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. + * + * Context: Acquires the 'clk_rpm_list_lock' and returns with the lock held on + * success. Otherwise the lock is released on failure. + * + * Return: 0 on success, negative errno otherwise. + */ +static int clk_pm_runtime_get_all(void) +{ + int ret; + struct clk_core *core, *failed; + + /* + * Grab the list lock to prevent any new clks from being registered + * or unregistered until clk_pm_runtime_put_all(). + */ + 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", + dev_name(failed->dev), failed->name); + goto err; + } + } + + return 0; + +err: + 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; +} + +/** + * clk_pm_runtime_put_all() - Runtime "put" all clk provider devices + * + * Put the runtime PM references taken in clk_pm_runtime_get_all() and release + * the 'clk_rpm_list_lock'. + */ +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 void clk_pm_runtime_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) { @@ -1362,9 +1450,6 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core) if (core->flags & CLK_IGNORE_UNUSED) return;
- if (clk_pm_runtime_get(core)) - return; - if (clk_core_is_prepared(core)) { trace_clk_unprepare(core); if (core->ops->unprepare_unused) @@ -1373,8 +1458,6 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core) core->ops->unprepare(core->hw); trace_clk_unprepare_complete(core); } - - clk_pm_runtime_put(core); }
static void __init clk_disable_unused_subtree(struct clk_core *core) @@ -1390,9 +1473,6 @@ static void __init clk_disable_unused_subtree(struct clk_core *core) if (core->flags & CLK_OPS_PARENT_ENABLE) clk_core_prepare_enable(core->parent);
- if (clk_pm_runtime_get(core)) - goto unprepare_out; - flags = clk_enable_lock();
if (core->enable_count) @@ -1417,8 +1497,6 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
unlock_out: clk_enable_unlock(flags); - clk_pm_runtime_put(core); -unprepare_out: if (core->flags & CLK_OPS_PARENT_ENABLE) clk_core_disable_unprepare(core->parent); } @@ -1434,6 +1512,7 @@ __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"); @@ -1442,6 +1521,13 @@ 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) @@ -1458,6 +1544,8 @@ static int __init clk_disable_unused(void)
clk_prepare_unlock();
+ clk_pm_runtime_put_all(); + return 0; } late_initcall_sync(clk_disable_unused); @@ -4195,6 +4283,12 @@ 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); @@ -4234,9 +4328,8 @@ __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_pm_runtime_init(core); core->of_node = np; if (dev && dev->driver) core->owner = dev->driver->owner;