CVE-2024-27004: In the Linux kernel, the following vulnerability has been resolved:  clk: Get runtime PM before walking tree during disable_unused  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 ---truncated---