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hrtimer: Remove HRTIMER_STATE_MIGRATE 

I do not understand HRTIMER_STATE_MIGRATE. Unless I am totally
confused it looks buggy and simply unneeded.

migrate_hrtimer_list() sets it to keep hrtimer_active() == T, but this
is not enough: this can fool, say, hrtimer_is_queued() in
dequeue_signal().

Can't migrate_hrtimer_list() simply use HRTIMER_STATE_ENQUEUED?
This fixes the race and we can kill STATE_MIGRATE.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: ktkhai@parallels.com
Cc: rostedt@goodmis.org
Cc: juri.lelli@gmail.com
Cc: pang.xunlei@linaro.org
Cc: wanpeng.li@linux.intel.com
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150611124743.072387650@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Oleg Nesterov 2015-06-11 14:46:44 +02:00 committed by Thomas Gleixner
parent 51a16c1e88
commit c04dca02bc
2 changed files with 3 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/hrtimer.h
View File

@ -70,17 +70,13 @@ enum hrtimer_restart {
* the handling of the timer.
*
* The HRTIMER_STATE_ENQUEUED bit is always or'ed to the current state
* to preserve the HRTIMER_STATE_CALLBACK in the above scenario. This
* also affects HRTIMER_STATE_MIGRATE where the preservation is not
* necessary. HRTIMER_STATE_MIGRATE is cleared after the timer is
* enqueued on the new cpu.
* to preserve the HRTIMER_STATE_CALLBACK in the above scenario.
*
* All state transitions are protected by cpu_base->lock.
*/
#define HRTIMER_STATE_INACTIVE 0x00
#define HRTIMER_STATE_ENQUEUED 0x01
#define HRTIMER_STATE_CALLBACK 0x02
#define HRTIMER_STATE_MIGRATE 0x04
/**
* struct hrtimer - the basic hrtimer structure

7
kernel/time/hrtimer.c
View File

@ -1508,11 +1508,11 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
debug_deactivate(timer);
/*
* Mark it as STATE_MIGRATE not INACTIVE otherwise the
* Mark it as ENQUEUED not INACTIVE otherwise the
* timer could be seen as !active and just vanish away
* under us on another CPU
*/
__remove_hrtimer(timer, old_base, HRTIMER_STATE_MIGRATE, 0);
__remove_hrtimer(timer, old_base, HRTIMER_STATE_ENQUEUED, 0);
timer->base = new_base;
/*
* Enqueue the timers on the new cpu. This does not
@ -1523,9 +1523,6 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
* event device.
*/
enqueue_hrtimer(timer, new_base);
/* Clear the migration state bit */
timer->state &= ~HRTIMER_STATE_MIGRATE;
}
}