linux-kernel - [PATCH 1/3] hrtimer: kill HRTIMER_STATE_MIGRATE, fix the race with hrtimer_is

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Message-ID: <20150608151059.GB23138@redhat.com>
Date:	Mon, 8 Jun 2015 17:10:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	umgwanakikbuti@...il.com, mingo@...e.hu, ktkhai@...allels.com,
	rostedt@...dmis.org, tglx@...utronix.de, juri.lelli@...il.com,
	pang.xunlei@...aro.org, wanpeng.li@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] hrtimer: kill HRTIMER_STATE_MIGRATE, fix the race with
	hrtimer_is_queued()

migrate_hrtimer_list() sets HRTIMER_STATE_MIGRATE to avoid the
race with hrtimer_active(), but this can't avoid the same race
with hrtimer_is_queued().

Kill HRTIMER_STATE_MIGRATE, we can simply use STATE_ENQUEUED.
---
 include/linux/hrtimer.h |    6 +-----
 kernel/time/hrtimer.c   |    7 ++-----
 2 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 05f6df1..44810bc 100644
--- a/include/linux/hrtimer.h
+++ b/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
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 76d4bd9..005fd44 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1640,11 +1640,11 @@ 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
@@ -1655,9 +1655,6 @@ 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;
 	}
 }
 
-- 
1.5.5.1


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