diff options
| author | Pingfan Liu <kernelfans@gmail.com> | 2018-07-31 16:51:32 +0800 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2018-08-06 12:35:20 +0200 |
| commit | 55f2503c3b69328735e88031ff8d6ba291bd952b (patch) | |
| tree | c89f476f4866d1e3ee11aa8b8601c68a23e3b025 /Documentation/power/freezing-of-tasks.txt | |
| parent | 82837ad5bda79cd13d64b9abad92e7872a06bc65 (diff) | |
PM / reboot: Eliminate race between reboot and suspend
At present, "systemctl suspend" and "shutdown" can run in parrallel. A
system can suspend after devices_shutdown(), and resume. Then the shutdown
task goes on to power off. This causes many devices are not really shut
off. Hence replacing reboot_mutex with system_transition_mutex (renamed
from pm_mutex) to achieve the exclusion. The renaming of pm_mutex as
system_transition_mutex can be better to reflect the purpose of the mutex.
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'Documentation/power/freezing-of-tasks.txt')
| -rw-r--r-- | Documentation/power/freezing-of-tasks.txt | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index af005770e767..cd283190855a 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -204,26 +204,26 @@ VI. Are there any precautions to be taken to prevent freezing failures? Yes, there are. -First of all, grabbing the 'pm_mutex' lock to mutually exclude a piece of code +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 'pm_mutex' is deemed necessary, -it is strongly discouraged to directly call mutex_[un]lock(&pm_mutex) since +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 'pm_mutex' lock, and hence that other entity failed +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 'pm_mutex', which will be released +"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(&pm_mutex). That would prevent freezing failures. +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 |