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SubjectRe: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the timer
On 06/05, Peter Zijlstra wrote:
>
> #define HRTIMER_STATE_INACTIVE 0x00
> #define HRTIMER_STATE_ENQUEUED 0x01
> -#define HRTIMER_STATE_CALLBACK 0x02
> -#define HRTIMER_STATE_MIGRATE 0x04
> +#define HRTIMER_STATE_MIGRATE 0x02

Slightly pff-topic, but I do not understand HRTIMER_STATE_MIGRATE
with or without this change. 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.

Oleg.


--- x/include/linux/hrtimer.h
+++ x/include/linux/hrtimer.h
@@ -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
--- x/kernel/time/hrtimer.c
+++ x/kernel/time/hrtimer.c
@@ -1642,11 +1642,11 @@ static void migrate_hrtimer_list(struct
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
@@ -1657,9 +1657,6 @@ static void migrate_hrtimer_list(struct
* event device.
*/
enqueue_hrtimer(timer, new_base);
-
- /* Clear the migration state bit */
- timer->state &= ~HRTIMER_STATE_MIGRATE;
}
}



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