linux-kernel - [PATCH] timerfd: really wake up processes when timer is cancelled on clock change

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Message-Id: <1307134425.16492.104.camel@w-amax.beaverton.ibm.com>
Date:	Fri, 03 Jun 2011 13:53:45 -0700
From:	Max Asbock <masbock@...ux.vnet.ibm.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	tglx <tglx@...utronix.de>, kay.sievers@...y.org,
	virtuoso@...nd.org, johnstul <johnstul@...ux.vnet.ibm.com>
Subject: [PATCH] timerfd: really wake up processes when timer is cancelled
	on clock change

When the system time is set the clock_was_set() function calls
timerfd_clock_was_set() to cancel and wake up processes waiting on
potential cancelable timerfd timers. However the wake up currently has
no effect because in the case of timerfd_read it is dependent on
ctx->ticks not being 0. timerfd_poll also requires ctx->ticks being non
zero. As a consequence processes waiting on cancelable timers only get
woken up when the timers expire. This patch fixes this by incrementing
ctx->ticks before calling wake_up.

Signed-off-by: Max Asbock <masbock@...ux.vnet.ibm.com>
---

--- linux-3.0-rc1/fs/timerfd.c
+++ linux-3.0-rc1.timerfd/fs/timerfd.c
@@ -61,7 +61,9 @@ static enum hrtimer_restart timerfd_tmrp
 
 /*
  * Called when the clock was set to cancel the timers in the cancel
- * list.
+ * list. This will wake up processes waiting on these timers. The
+ * wake-up requires ctx->ticks to be non zero, therefore we increment
+ * it before calling wake_up_locked().
  */
 void timerfd_clock_was_set(void)
 {
@@ -76,6 +78,7 @@ void timerfd_clock_was_set(void)
 		spin_lock_irqsave(&ctx->wqh.lock, flags);
 		if (ctx->moffs.tv64 != moffs.tv64) {
 			ctx->moffs.tv64 = KTIME_MAX;
+			ctx->ticks++;
 			wake_up_locked(&ctx->wqh);
 		}
 		spin_unlock_irqrestore(&ctx->wqh.lock, flags);


-- 
Max Asböck


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