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Subject[PATCH] [3/10] x86: MCE: Always use separate work queue to run trigger
Date

Impact: Needed for bug fix in next patch

This relaxes the requirement that mce_notify_user has to run in process
context. Useful for future changes, but also leads to cleaner
behaviour now. Now instead mce_notify_user can be called directly
from interrupt (but not NMI) context.

The work queue only uses a single global work struct, which can be done safely
because it is always free to reuse before the trigger function is executed.
This way no events can be lost.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
arch/x86/kernel/cpu/mcheck/mce_64.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)

Index: linux/arch/x86/kernel/cpu/mcheck/mce_64.c
===================================================================
--- linux.orig/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-02-12 11:30:51.000000000 +0100
+++ linux/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-02-12 12:10:21.000000000 +0100
@@ -380,11 +380,17 @@
schedule_delayed_work(&mcheck_work, next_interval);
}

+static void mce_do_trigger(struct work_struct *work)
+{
+ call_usermodehelper(trigger, trigger_argv, NULL, UMH_NO_WAIT);
+}
+
+static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
+
/*
- * This is only called from process context. This is where we do
- * anything we need to alert userspace about new MCEs. This is called
- * directly from the poller and also from entry.S and idle, thanks to
- * TIF_MCE_NOTIFY.
+ * Notify the user(s) about new machine check events.
+ * Can be called from interrupt context, but not from machine check/NMI
+ * context.
*/
int mce_notify_user(void)
{
@@ -394,9 +400,14 @@
unsigned long now = jiffies;

wake_up_interruptible(&mce_wait);
- if (trigger[0])
- call_usermodehelper(trigger, trigger_argv, NULL,
- UMH_NO_WAIT);
+
+ /*
+ * There is no risk of missing notifications because
+ * work_pending is always cleared before the function is
+ * executed.
+ */
+ if (trigger[0] && !work_pending(&mce_trigger_work))
+ schedule_work(&mce_trigger_work);

if (time_after_eq(now, last_print + (check_interval*HZ))) {
last_print = now;

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