linux-kernel - [PATCH 6/9] watchdog: implement error handling for failure to set up hardware perf events

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Message-Id: <1423168825-156238-7-git-send-email-dzickus@redhat.com>
Date:	Thu,  5 Feb 2015 15:40:22 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Don Zickus <dzickus@...hat.com>
Subject: [PATCH 6/9] watchdog: implement error handling for failure to set up hardware perf events

From: Ulrich Obergfell <uobergfe@...hat.com>

If watchdog_nmi_enable() fails to set up the hardware perf event
of one CPU, the entire hard lockup detector is deemed unreliable.
Hence, disable the hard lockup detector and shut down the hardware
perf events on all CPUs.

Signed-off-by: Ulrich Obergfell <uobergfe@...hat.com>
Signed-off-by: Don Zickus <dzickus@...hat.com>
---
 kernel/watchdog.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 26002ed..7ad8949 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -502,6 +502,15 @@ static void watchdog(unsigned int cpu)
 	__this_cpu_write(soft_lockup_hrtimer_cnt,
 			 __this_cpu_read(hrtimer_interrupts));
 	__touch_watchdog();
+
+	/*
+	 * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
+	 * failure path. Check for failures that can occur asynchronously -
+	 * for example, when CPUs are on-lined - and shut down the hardware
+	 * perf event on each CPU accordingly.
+	 */
+	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
+		watchdog_nmi_disable(cpu);
 }
 
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
@@ -552,6 +561,15 @@ handle_err:
 		goto out_save;
 	}
 
+	/*
+	 * Disable the hard lockup detector if _any_ CPU fails to set up
+	 * set up the hardware perf event. The watchdog() function checks
+	 * the NMI_WATCHDOG_ENABLED bit periodically.
+	 */
+	smp_mb__before_atomic();
+	clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
+	smp_mb__after_atomic();
+
 	/* skip displaying the same error again */
 	if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 		return PTR_ERR(event);
-- 
1.7.1

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