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Subject[RFC PATCH 12/23] kernel/watchdog: Introduce a struct for NMI watchdog operations
Date
Instead of exposing individual functions for the operations of the NMI
watchdog, define a common interface that can be used across multiple
implementations.

The struct nmi_watchdog_ops is defined for such operations. These initial
definitions include the enable, disable, start, stop, and cleanup
operations.

Only a single NMI watchdog can be used in the system. The operations of
this NMI watchdog are accessed via the new variable nmi_wd_ops. This
variable is set to point the operations of the first NMI watchdog that
initializes successfully. Even though at this moment, the only available
NMI watchdog is the perf-based hardlockup detector. More implementations
can be added in the future.

While introducing this new struct for the NMI watchdog operations, convert
the perf-based NMI watchdog to use these operations.

The functions hardlockup_detector_perf_restart() and
hardlockup_detector_perf_stop() are special. They are not regular watchdog
operations; they are used to work around hardware bugs. Thus, they are not
used for the start and stop operations. Furthermore, the perf-based NMI
watchdog does not need to implement such operations. They are intended to
globally start and stop the NMI watchdog; the perf-based NMI
watchdog is implemented on a per-CPU basis.

Currently, when perf-based hardlockup detector is not selected at build
time, a dummy hardlockup_detector_perf_init() is used. The return value
of this function depends on CONFIG_HAVE_NMI_WATCHDOG. This behavior is
conserved by defining using the set of NMI watchdog operations structure
hardlockup_detector_noop. These dummy operations are used when no hard-
lockup detector is used or fails to initialize.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Andi Kleen <andi.kleen@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jacob Pan <jacob.jun.pan@intel.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Babu Moger <babu.moger@oracle.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
Cc: x86@kernel.org
Cc: sparclinux@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: iommu@lists.linux-foundation.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
include/linux/nmi.h | 39 +++++++++++++++++++++++++++----------
kernel/watchdog.c | 54 +++++++++++++++++++++++++++++++++++++++++++++------
kernel/watchdog_hld.c | 16 +++++++++++----
3 files changed, 89 insertions(+), 20 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index b8d868d..d3f5d55f 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -92,24 +92,43 @@ static inline void hardlockup_detector_disable(void) {}
extern void arch_touch_nmi_watchdog(void);
extern void hardlockup_detector_perf_stop(void);
extern void hardlockup_detector_perf_restart(void);
-extern void hardlockup_detector_perf_disable(void);
-extern void hardlockup_detector_perf_enable(void);
-extern void hardlockup_detector_perf_cleanup(void);
-extern int hardlockup_detector_perf_init(void);
#else
static inline void hardlockup_detector_perf_stop(void) { }
static inline void hardlockup_detector_perf_restart(void) { }
-static inline void hardlockup_detector_perf_disable(void) { }
-static inline void hardlockup_detector_perf_enable(void) { }
-static inline void hardlockup_detector_perf_cleanup(void) { }
# if !defined(CONFIG_HAVE_NMI_WATCHDOG)
-static inline int hardlockup_detector_perf_init(void) { return -ENODEV; }
static inline void arch_touch_nmi_watchdog(void) {}
-# else
-static inline int hardlockup_detector_perf_init(void) { return 0; }
# endif
#endif

+/**
+ * struct nmi_watchdog_ops - Operations performed by NMI watchdogs
+ * @init: Initialize and configure the hardware resources of the
+ * NMI watchdog.
+ * @enable: Enable (i.e., monitor for hardlockups) the NMI watchdog
+ * in the CPU in which the function is executed.
+ * @disable: Disable (i.e., do not monitor for hardlockups) the NMI
+ * in the CPU in which the function is executed.
+ * @start: Start the the NMI watchdog in all CPUs. Used after the
+ * parameters of the watchdog are updated. Optional if
+ * such updates does not impact operation the NMI watchdog.
+ * @stop: Stop the the NMI watchdog in all CPUs. Used before the
+ * parameters of the watchdog are updated. Optional if
+ * such updates does not impact the NMI watchdog.
+ * @cleanup: Cleanup unneeded data structures of the NMI watchdog.
+ * Used after updating the parameters of the watchdog.
+ * Optional no cleanup is needed.
+ */
+struct nmi_watchdog_ops {
+ int (*init)(void);
+ void (*enable)(void);
+ void (*disable)(void);
+ void (*start)(void);
+ void (*stop)(void);
+ void (*cleanup)(void);
+};
+
+extern struct nmi_watchdog_ops hardlockup_detector_perf_ops;
+
void watchdog_nmi_stop(void);
void watchdog_nmi_start(void);
int watchdog_nmi_probe(void);
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 576d180..5057376 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -48,6 +48,8 @@ int __read_mostly soft_watchdog_user_enabled = 1;
int __read_mostly watchdog_thresh = 10;
int __read_mostly nmi_watchdog_available;

+static struct nmi_watchdog_ops *nmi_wd_ops;
+
struct cpumask watchdog_allowed_mask __read_mostly;

struct cpumask watchdog_cpumask __read_mostly;
@@ -99,6 +101,23 @@ __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
#endif /* CONFIG_HARDLOCKUP_DETECTOR */

/*
+ * Define a non-existent hard lockup detector. It will be used only if
+ * no actual hardlockup detector was selected at built time.
+ */
+static inline int noop_hardlockup_detector_init(void)
+{
+ /* If arch has an NMI watchdog, pretend to initialize it. */
+ if (IS_ENABLED(CONFIG_HAVE_NMI_WATCHDOG))
+ return 0;
+ else
+ return -ENODEV;
+}
+
+static struct nmi_watchdog_ops hardlockup_detector_noop = {
+ .init = noop_hardlockup_detector_init,
+};
+
+/*
* These functions can be overridden if an architecture implements its
* own hardlockup detector.
*
@@ -108,19 +127,33 @@ __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
*/
int __weak watchdog_nmi_enable(unsigned int cpu)
{
- hardlockup_detector_perf_enable();
+ if (nmi_wd_ops && nmi_wd_ops->enable)
+ nmi_wd_ops->enable();
+
return 0;
}

void __weak watchdog_nmi_disable(unsigned int cpu)
{
- hardlockup_detector_perf_disable();
+ if (nmi_wd_ops && nmi_wd_ops->disable)
+ nmi_wd_ops->disable();
}

/* Return 0, if a NMI watchdog is available. Error code otherwise */
int __weak __init watchdog_nmi_probe(void)
{
- return hardlockup_detector_perf_init();
+ int ret = -ENODEV;
+
+ if (IS_ENABLED(CONFIG_HARDLOCKUP_DETECTOR_PERF))
+ ret = hardlockup_detector_perf_ops.init();
+
+ if (!ret) {
+ nmi_wd_ops = &hardlockup_detector_perf_ops;
+ return ret;
+ }
+
+ nmi_wd_ops = &hardlockup_detector_noop;
+ return nmi_wd_ops->init();
}

/**
@@ -131,7 +164,11 @@ int __weak __init watchdog_nmi_probe(void)
* update_variables();
* watchdog_nmi_start();
*/
-void __weak watchdog_nmi_stop(void) { }
+void __weak watchdog_nmi_stop(void)
+{
+ if (nmi_wd_ops && nmi_wd_ops->stop)
+ nmi_wd_ops->stop();
+}

/**
* watchdog_nmi_start - Start the watchdog after reconfiguration
@@ -144,7 +181,11 @@ void __weak watchdog_nmi_stop(void) { }
* - watchdog_thresh
* - watchdog_cpumask
*/
-void __weak watchdog_nmi_start(void) { }
+void __weak watchdog_nmi_start(void)
+{
+ if (nmi_wd_ops && nmi_wd_ops->start)
+ nmi_wd_ops->start();
+}

/**
* lockup_detector_update_enable - Update the sysctl enable bit
@@ -627,7 +668,8 @@ static inline void lockup_detector_setup(void)
static void __lockup_detector_cleanup(void)
{
lockdep_assert_held(&watchdog_mutex);
- hardlockup_detector_perf_cleanup();
+ if (nmi_wd_ops && nmi_wd_ops->cleanup)
+ nmi_wd_ops->cleanup();
}

/**
diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index e449a23..036cb0a 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -186,7 +186,7 @@ static int hardlockup_detector_event_create(void)
/**
* hardlockup_detector_perf_enable - Enable the local event
*/
-void hardlockup_detector_perf_enable(void)
+static void hardlockup_detector_perf_enable(void)
{
if (hardlockup_detector_event_create())
return;
@@ -201,7 +201,7 @@ void hardlockup_detector_perf_enable(void)
/**
* hardlockup_detector_perf_disable - Disable the local event
*/
-void hardlockup_detector_perf_disable(void)
+static void hardlockup_detector_perf_disable(void)
{
struct perf_event *event = this_cpu_read(watchdog_ev);

@@ -219,7 +219,7 @@ void hardlockup_detector_perf_disable(void)
*
* Called from lockup_detector_cleanup(). Serialized by the caller.
*/
-void hardlockup_detector_perf_cleanup(void)
+static void hardlockup_detector_perf_cleanup(void)
{
int cpu;

@@ -281,7 +281,7 @@ void __init hardlockup_detector_perf_restart(void)
/**
* hardlockup_detector_perf_init - Probe whether NMI event is available at all
*/
-int __init hardlockup_detector_perf_init(void)
+static int __init hardlockup_detector_perf_init(void)
{
int ret = hardlockup_detector_event_create();

@@ -291,5 +291,13 @@ int __init hardlockup_detector_perf_init(void)
perf_event_release_kernel(this_cpu_read(watchdog_ev));
this_cpu_write(watchdog_ev, NULL);
}
+
return ret;
}
+
+struct nmi_watchdog_ops hardlockup_detector_perf_ops = {
+ .init = hardlockup_detector_perf_init,
+ .enable = hardlockup_detector_perf_enable,
+ .disable = hardlockup_detector_perf_disable,
+ .cleanup = hardlockup_detector_perf_cleanup,
+};
--
2.7.4
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