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Subject[patch V2 05/29] lockup_detector: Remove broken suspend/resume interfaces
This interface has several issues:

- It's causing recursive locking of the hotplug lock.

- It's complete overkill to teardown all threads and then recreate them

The same can be achieved with the simple hardlockup_detector_perf_stop /
restart() interfaces. The abuse from the busy looping poweroff() loop of
PARISC has been solved as well.

Remove the cruft.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20170831073053.359128818@linutronix.de

---
arch/powerpc/kernel/watchdog.c | 3 -
include/linux/nmi.h | 12 -----
kernel/watchdog.c | 89 -----------------------------------------
3 files changed, 1 insertion(+), 103 deletions(-)

--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -310,9 +310,6 @@ static int start_wd_on_cpu(unsigned int
if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
return 0;

- if (watchdog_suspended)
- return 0;
-
if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
return 0;

--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -164,7 +164,6 @@ extern int watchdog_thresh;
extern unsigned long watchdog_enabled;
extern struct cpumask watchdog_cpumask;
extern unsigned long *watchdog_cpumask_bits;
-extern int __read_mostly watchdog_suspended;
#ifdef CONFIG_SMP
extern int sysctl_softlockup_all_cpu_backtrace;
extern int sysctl_hardlockup_all_cpu_backtrace;
@@ -192,17 +191,6 @@ extern int proc_watchdog_thresh(struct c
void __user *, size_t *, loff_t *);
extern int proc_watchdog_cpumask(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
-extern int lockup_detector_suspend(void);
-extern void lockup_detector_resume(void);
-#else
-static inline int lockup_detector_suspend(void)
-{
- return 0;
-}
-
-static inline void lockup_detector_resume(void)
-{
-}
#endif

#ifdef CONFIG_HAVE_ACPI_APEI_NMI
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -97,19 +97,6 @@ unsigned long *watchdog_cpumask_bits = c
* unregistered/stopped, so it is an indicator whether the threads exist.
*/
static int __read_mostly watchdog_running;
-/*
- * If a subsystem has a need to deactivate the watchdog temporarily, it
- * can use the suspend/resume interface to achieve this. The content of
- * the 'watchdog_suspended' variable reflects this state. Existing threads
- * are parked/unparked by the lockup_detector_{suspend|resume} functions
- * (see comment blocks pertaining to those functions for further details).
- *
- * 'watchdog_suspended' also prevents threads from being registered/started
- * or unregistered/stopped via parameters in /proc/sys/kernel, so the state
- * of 'watchdog_running' cannot change while the watchdog is deactivated
- * temporarily (see related code in 'proc' handlers).
- */
-int __read_mostly watchdog_suspended;

/*
* These functions can be overridden if an architecture implements its
@@ -136,7 +123,6 @@ void __weak watchdog_nmi_disable(unsigne
* - watchdog_cpumask
* - sysctl_hardlockup_all_cpu_backtrace
* - hardlockup_panic
- * - watchdog_suspended
*/
void __weak watchdog_nmi_reconfigure(void)
{
@@ -672,61 +658,6 @@ void lockup_detector_soft_poweroff(void)
watchdog_enabled = 0;
}

-/*
- * Suspend the hard and soft lockup detector by parking the watchdog threads.
- */
-int lockup_detector_suspend(void)
-{
- int ret = 0;
-
- get_online_cpus();
- mutex_lock(&watchdog_proc_mutex);
- /*
- * Multiple suspend requests can be active in parallel (counted by
- * the 'watchdog_suspended' variable). If the watchdog threads are
- * running, the first caller takes care that they will be parked.
- * The state of 'watchdog_running' cannot change while a suspend
- * request is active (see related code in 'proc' handlers).
- */
- if (watchdog_running && !watchdog_suspended)
- ret = watchdog_park_threads();
-
- if (ret == 0)
- watchdog_suspended++;
- else {
- watchdog_disable_all_cpus();
- pr_err("Failed to suspend lockup detectors, disabled\n");
- watchdog_enabled = 0;
- }
-
- watchdog_nmi_reconfigure();
-
- mutex_unlock(&watchdog_proc_mutex);
-
- return ret;
-}
-
-/*
- * Resume the hard and soft lockup detector by unparking the watchdog threads.
- */
-void lockup_detector_resume(void)
-{
- mutex_lock(&watchdog_proc_mutex);
-
- watchdog_suspended--;
- /*
- * The watchdog threads are unparked if they were previously running
- * and if there is no more active suspend request.
- */
- if (watchdog_running && !watchdog_suspended)
- watchdog_unpark_threads();
-
- watchdog_nmi_reconfigure();
-
- mutex_unlock(&watchdog_proc_mutex);
- put_online_cpus();
-}
-
#ifdef CONFIG_SYSCTL

/*
@@ -775,12 +706,6 @@ static int proc_watchdog_common(int whic
get_online_cpus();
mutex_lock(&watchdog_proc_mutex);

- if (watchdog_suspended) {
- /* no parameter changes allowed while watchdog is suspended */
- err = -EAGAIN;
- goto out;
- }
-
/*
* If the parameter is being read return the state of the corresponding
* bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
@@ -872,12 +797,6 @@ int proc_watchdog_thresh(struct ctl_tabl
get_online_cpus();
mutex_lock(&watchdog_proc_mutex);

- if (watchdog_suspended) {
- /* no parameter changes allowed while watchdog is suspended */
- err = -EAGAIN;
- goto out;
- }
-
old = ACCESS_ONCE(watchdog_thresh);
err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

@@ -917,12 +836,6 @@ int proc_watchdog_cpumask(struct ctl_tab
get_online_cpus();
mutex_lock(&watchdog_proc_mutex);

- if (watchdog_suspended) {
- /* no parameter changes allowed while watchdog is suspended */
- err = -EAGAIN;
- goto out;
- }
-
err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
if (!err && write) {
/* Remove impossible cpus to keep sysctl output cleaner. */
@@ -941,7 +854,7 @@ int proc_watchdog_cpumask(struct ctl_tab

watchdog_nmi_reconfigure();
}
-out:
+
mutex_unlock(&watchdog_proc_mutex);
put_online_cpus();
return err;

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