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Diffstat (limited to 'Documentation/power/freezing-of-tasks.rst')
| -rw-r--r-- | Documentation/power/freezing-of-tasks.rst | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/Documentation/power/freezing-of-tasks.rst b/Documentation/power/freezing-of-tasks.rst index ef110fe55e82..8bd693399834 100644 --- a/Documentation/power/freezing-of-tasks.rst +++ b/Documentation/power/freezing-of-tasks.rst @@ -215,30 +215,31 @@ VI. Are there any precautions to be taken to prevent freezing failures? Yes, there are. -First of all, grabbing the 'system_transition_mutex' lock to mutually exclude a piece of code -from system-wide sleep such as suspend/hibernation is not encouraged. -If possible, that piece of code must instead hook onto the suspend/hibernation -notifiers to achieve mutual exclusion. Look at the CPU-Hotplug code -(kernel/cpu.c) for an example. - -However, if that is not feasible, and grabbing 'system_transition_mutex' is deemed necessary, -it is strongly discouraged to directly call mutex_[un]lock(&system_transition_mutex) since -that could lead to freezing failures, because if the suspend/hibernate code -successfully acquired the 'system_transition_mutex' lock, and hence that other entity failed -to acquire the lock, then that task would get blocked in TASK_UNINTERRUPTIBLE -state. As a consequence, the freezer would not be able to freeze that task, -leading to freezing failure. +First of all, grabbing the 'system_transition_mutex' lock to mutually exclude a +piece of code from system-wide sleep such as suspend/hibernation is not +encouraged. If possible, that piece of code must instead hook onto the +suspend/hibernation notifiers to achieve mutual exclusion. Look at the +CPU-Hotplug code (kernel/cpu.c) for an example. + +However, if that is not feasible, and grabbing 'system_transition_mutex' is +deemed necessary, it is strongly discouraged to directly call +mutex_[un]lock(&system_transition_mutex) since that could lead to freezing +failures, because if the suspend/hibernate code successfully acquired the +'system_transition_mutex' lock, and hence that other entity failed to acquire +the lock, then that task would get blocked in TASK_UNINTERRUPTIBLE state. As a +consequence, the freezer would not be able to freeze that task, leading to +freezing failure. However, the [un]lock_system_sleep() APIs are safe to use in this scenario, since they ask the freezer to skip freezing this task, since it is anyway -"frozen enough" as it is blocked on 'system_transition_mutex', which will be released -only after the entire suspend/hibernation sequence is complete. -So, to summarize, use [un]lock_system_sleep() instead of directly using +"frozen enough" as it is blocked on 'system_transition_mutex', which will be +released only after the entire suspend/hibernation sequence is complete. So, to +summarize, use [un]lock_system_sleep() instead of directly using mutex_[un]lock(&system_transition_mutex). That would prevent freezing failures. V. Miscellaneous ================ /sys/power/pm_freeze_timeout controls how long it will cost at most to freeze -all user space processes or all freezable kernel threads, in unit of millisecond. -The default value is 20000, with range of unsigned integer. +all user space processes or all freezable kernel threads, in unit of +millisecond. The default value is 20000, with range of unsigned integer. |