linux/kernel/time/clocksource.c, branch v2.6.32

clocksource: Resume clocksource without taking the clocksource mutex

2009-09-24T20:37:53Z

git commit 75c5158f70c065b9 converted the clocksource spinlock to a mutex. This causes the following BUG: BUG: sleeping function called from invalid context at kernel/mutex.c:280 in_atomic(): 0, irqs_disabled(): 1, pid: 2473, name: pm-suspend 2 locks held by pm-suspend/2473: #0: (&buffer->mutex){......}, at: [] sysfs_write_file+0x3c/0x137 #1: (pm_mutex){......}, at: [] enter_state+0x39/0x130 Pid: 2473, comm: pm-suspend Not tainted 2.6.31 #1 Call Trace: [] ? __debug_show_held_locks+0x22/0x24 [] __might_sleep+0x107/0x10b [] mutex_lock_nested+0x25/0x43 [] clocksource_resume+0x1c/0x60 [] timekeeping_resume+0x1e/0x1c8 [] __sysdev_resume+0x25/0xcf [] sysdev_resume+0x6d/0xae [] suspend_devices_and_enter+0x12b/0x1af [] enter_state+0xdf/0x130 [] state_store+0xb6/0xd3 [] kobj_attr_store+0x17/0x19 [] sysfs_write_file+0xfb/0x137 [] vfs_write+0xae/0x10b [] ? __up_read+0x1a/0x7f [] sys_write+0x4a/0x6e [] system_call_fastpath+0x16/0x1b clocksource_resume is called early in the resume process, there is only one cpu, no processes are running and the interrupts are disabled. It is therefore possible to resume the clocksources without taking the clocksource mutex. Reported-by: Xiaotian Feng Signed-off-by: Martin Schwidefsky Tested-by: Michal Schmidt Cc: Xiaotian Feng Cc: John Stultz LKML-Reference: <20090924172952.49697825@mschwide.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar

clocksource: Delay clocksource down rating to late boot

2009-09-14T19:59:32Z

The down rating of clock sources in the early boot process via the clock source watchdog mechanism can happen way before the per cpu event queues are initialized. This leads to a boot crash on x86 when the TSC is marked unstable in the SMP bring up. The selection of a clock source for time keeping happens in the late boot process so we can safely delay the list manipulation until clocksource_done_booting() is called. Signed-off-by: Thomas Gleixner LKML-Reference: Cc: Martin Schwidefsky

clocksource: clocksource_select must be called with mutex locked

2009-09-14T19:59:32Z

The callers of clocksource_select must hold clocksource_mutex to protect the clocksource_list. Signed-off-by: Thomas Gleixner LKML-Reference: Cc: Martin Schwidefsky

clocksource: Resolve cpu hotplug dead lock with TSC unstable, fix crash

2009-09-11T18:17:18Z

The watchdog timer is started after the watchdog clocksource and at least one watched clocksource have been registered. The clocksource work element watchdog_work is initialized just before the clocksource timer is started. This is too late for the clocksource_mark_unstable call from native_cpu_up. To fix this use a static initializer for watchdog_work. This resolves a boot crash reported by multiple people. Signed-off-by: Martin Schwidefsky Cc: Jens Axboe Cc: John Stultz LKML-Reference: <20090911153305.3fe9a361@skybase> Signed-off-by: Ingo Molnar

clocksource: Resolve cpu hotplug dead lock with TSC unstable

2009-08-28T18:25:24Z

Martin Schwidefsky analyzed it: To register a clocksource the clocksource_mutex is acquired and if necessary timekeeping_notify is called to install the clocksource as the timekeeper clock. timekeeping_notify uses stop_machine which needs to take cpu_add_remove_lock mutex. Starting a new cpu is done with the cpu_add_remove_lock mutex held. native_cpu_up checks the tsc of the new cpu and if the tsc is no good clocksource_change_rating is called. Which needs the clocksource_mutex and the deadlock is complete. The solution is to replace the TSC via the clocksource watchdog mechanism. Mark the TSC as unstable and schedule the watchdog work so it gets removed in the watchdog thread context. Signed-off-by: Thomas Gleixner LKML-Reference: Cc: Martin Schwidefsky Cc: John Stultz

clocksource: Avoid clocksource watchdog circular locking dependency

2009-08-19T10:00:56Z

stop_machine from a multithreaded workqueue is not allowed because of a circular locking dependency between cpu_down and the workqueue execution. Use a kernel thread to do the clocksource downgrade. Signed-off-by: Martin Schwidefsky Cc: Peter Zijlstra Cc: john stultz LKML-Reference: <20090818170942.3ab80c91@skybase> Signed-off-by: Thomas Gleixner

clocksource: Protect the watchdog rating changes with clocksource_mutex

2009-08-19T09:42:48Z

Martin pointed out that commit 6ea41d2529 (clocksource: Call clocksource_change_rating() outside of watchdog_lock) has a theoretical reference count problem. The calls to clocksource_change_rating() are now done outside of the clocksource mutex and outside of the watchdog lock. A concurrent clocksource_unregister() could remove the clock. Split out the code which changes the rating from clocksource_change_rating() into __clocksource_change_rating(). Protect the clocksource_watchdog_work() code sequence with the clocksource_mutex() and call __clocksource_change_rating(). LKML-Reference: Signed-off-by: Thomas Gleixner Cc: Martin Schwidefsky

clocksource: Call clocksource_change_rating() outside of watchdog_lock

2009-08-15T11:20:42Z

The changes to the watchdog logic introduced a lock inversion between watchdog_lock and clocksource_mutex. Change the rating outside of watchdog_lock to avoid it. Signed-off-by: Thomas Gleixner

timekeeping: Update clocksource with stop_machine

2009-08-15T08:55:46Z

update_wall_time calls change_clocksource HZ times per second to check if a new clock source is available. In close to 100% of all calls there is no new clock. Replace the tick based check by an update done with stop_machine. Signed-off-by: Martin Schwidefsky Cc: Ingo Molnar Acked-by: John Stultz Cc: Daniel Walker LKML-Reference: <20090814134810.711836357@de.ibm.com> Signed-off-by: Thomas Gleixner

timekeeping: Introduce struct timekeeper

2009-08-15T08:55:46Z

Add struct timekeeper to keep the internal values timekeeping.c needs in regard to the currently selected clock source. This moves the timekeeping intervals, xtime_nsec and the ntp error value from struct clocksource to struct timekeeper. The raw_time is removed from the clocksource as well. It gets treated like xtime as a global variable. Eventually xtime raw_time should be moved to struct timekeeper. [ tglx: minor cleanup ] Signed-off-by: Martin Schwidefsky Cc: Ingo Molnar Acked-by: John Stultz Cc: Daniel Walker LKML-Reference: <20090814134809.613209842@de.ibm.com> Signed-off-by: Thomas Gleixner