Patchwork [1/2,LUCID] (pre-upstream) Fix clock_was_set so it is safe to call from atomic

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Submitter Brad Figg
Date July 3, 2012, 2:17 a.m.
Message ID <1341281876-28601-2-git-send-email-brad.figg@canonical.com>
Download mbox | patch
Permalink /patch/168671/
State New
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Comments

Brad Figg - July 3, 2012, 2:17 a.m.
From: John Stultz <john.stultz@linaro.org>

BugLink: http://bugs.launchpad.net/bugs/1020285

Backport for 2.6.32.59

NOTE:This is a prerequisite patch that's required to
address the widely observed leap-second related futex/hrtimer
issues.

Currently clock_was_set() is unsafe to be called from atomic
context, as it calls on_each_cpu(). This causes problems when
we need to adjust the time from update_wall_time().

To fix this, introduce a work_struct so if we're in_atomic,
we can schedule work to do the necessary update after we're
out of the atomic section.

CC: Prarit Bhargava <prarit@redhat.com>
CC: stable@vger.kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Brad Figg <brad.figg@canonical.com>
---
 kernel/hrtimer.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

Patch

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index a6e9d00..307c4e4 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -647,11 +647,26 @@  static void retrigger_next_event(void *arg)
  * resolution timer interrupts. On UP we just disable interrupts and
  * call the high resolution interrupt code.
  */
-void clock_was_set(void)
+static void do_clock_was_set(struct work_struct *work)
 {
 	/* Retrigger the CPU local events everywhere */
 	on_each_cpu(retrigger_next_event, NULL, 1);
 }
+static DECLARE_WORK(clock_was_set_work, do_clock_was_set);
+
+void clock_was_set(void)
+{
+	/*
+	 * We can't call on_each_cpu() from atomic context,
+	 * so if we're in_atomic, schedule the clock_was_set
+	 * for later.
+	 */
+	if (in_atomic())
+		schedule_work(&clock_was_set_work);
+	else
+		do_clock_was_set(NULL);
+}
+
 
 /*
  * During resume we might have to reprogram the high resolution timer