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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Sebastian Siewior <bigeasy@linutronix.de>,
	Nicholas Piggin <npiggin@gmail.com>,
	Don Zickus <dzickus@redhat.com>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	Ulrich Obergfell <uobergfe@redhat.com>
Subject: [patch V2 05/29] lockup_detector: Remove broken suspend/resume interfaces
Date: Tue, 12 Sep 2017 21:36:59 +0200
Message-ID: <20170912194146.487537732@linutronix.de> (raw)
In-Reply-To: <20170912193654.321505854@linutronix.de>


[-- Attachment #0: lockup_detector_Remove_broken_suspendresume_interfaces.patch --]
[-- Type: text/plain, Size: 6296 bytes --]

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;

  parent reply index

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-12 19:36 [patch V2 00/29] lockup_detector: Cure hotplug deadlocks and replace duct tape Thomas Gleixner
2017-09-12 19:36 ` [patch V2 01/29] hardlockup_detector: Provide interface to stop/restart perf events Thomas Gleixner
2017-09-14 10:40   ` [tip:core/urgent] watchdog/hardlockup: " tip-bot for Peter Zijlstra
2017-09-12 19:36 ` [patch V2 02/29] perf/x86/intel: Sanitize PMU HT bug workaround Thomas Gleixner
2017-09-14 10:40   ` [tip:core/urgent] perf/x86/intel, watchdog/core: " tip-bot for Peter Zijlstra
2017-09-12 19:36 ` [patch V2 03/29] lockup_detector: Provide interface to stop from poweroff() Thomas Gleixner
2017-09-14 10:40   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:36 ` [patch V2 04/29] parisc: Use lockup_detector_stop() Thomas Gleixner
2017-09-14  8:59   ` Helge Deller
2017-09-14 13:46     ` Don Zickus
2017-09-14 10:41   ` [tip:core/urgent] parisc, watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:36 ` Thomas Gleixner [this message]
2017-09-14 10:41   ` [tip:core/urgent] watchdog/core: Remove broken suspend/resume interfaces tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 06/29] lockup_detector: Rework cpu hotplug locking Thomas Gleixner
2017-09-14 10:41   ` [tip:core/urgent] watchdog/core: Rework CPU " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 07/29] lockup_detector: Rename watchdog_proc_mutex Thomas Gleixner
2017-09-14 10:42   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 08/29] lockup_detector: Mark hardlockup_detector_disable() __init Thomas Gleixner
2017-09-14 10:42   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 09/29] lockup_detector/perf: Remove broken self disable on failure Thomas Gleixner
2017-09-14 10:43   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 10/29] lockup_detector/perf: Prevent cpu hotplug deadlock Thomas Gleixner
2017-09-14 10:43   ` [tip:core/urgent] watchdog/hardlockup/perf: Prevent CPU " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 11/29] lockup_detector: Remove park_in_progress obfuscation Thomas Gleixner
2017-09-12 19:37 ` [patch V2 12/29] lockup_detector: Cleanup stub functions Thomas Gleixner
2017-09-14 10:44   ` [tip:core/urgent] watchdog/core: Clean up " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 13/29] lockup_detector: Cleanup the ifdef maze Thomas Gleixner
2017-09-14 10:44   ` [tip:core/urgent] watchdog/core: Clean up the #ifdef maze tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 14/29] lockup_detector: Split out cpumask write function Thomas Gleixner
2017-09-14 10:45   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 15/29] smpboot/threads: Avoid runtime allocation Thomas Gleixner
2017-09-14 10:45   ` [tip:core/urgent] smpboot/threads, watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 16/29] lockup_detector: Create new thread handling infrastructure Thomas Gleixner
2017-09-14 10:45   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 17/29] lockup_detector: Get rid of the thread teardown/setup dance Thomas Gleixner
2017-09-14 10:46   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 18/29] lockup_detector: Further simplify sysctl handling Thomas Gleixner
2017-09-14 10:46   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 19/29] lockup_detector: Cleanup header mess Thomas Gleixner
2017-09-14 10:47   ` [tip:core/urgent] watchdog/core: Clean up " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 20/29] lockup_detector/sysctl: Get rid of the ifdeffery Thomas Gleixner
2017-09-14 10:47   ` [tip:core/urgent] watchdog/sysctl: Get rid of the #ifdeffery tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 21/29] lockup_detector: Cleanup sysctl variable name space Thomas Gleixner
2017-09-14 10:47   ` [tip:core/urgent] watchdog/sysctl: Clean up " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 22/29] lockup_detector: Make watchdog_nmi_reconfigure() two stage Thomas Gleixner
2017-09-14 10:48   ` [tip:core/urgent] watchdog/core, powerpc: " tip-bot for Thomas Gleixner
2017-10-03  0:29   ` [patch V2 22/29] lockup_detector: " Michael Ellerman
2017-10-03  6:50     ` Thomas Gleixner
2017-10-03  7:04       ` Thomas Gleixner
2017-10-03 10:01         ` Nicholas Piggin
2017-10-03 10:56           ` Thomas Gleixner
2017-10-03 11:36       ` Michael Ellerman
2017-10-03 12:13         ` Thomas Gleixner
2017-10-03 13:20           ` Thomas Gleixner
2017-10-03 19:27             ` Thomas Gleixner
2017-10-04  5:53               ` Michael Ellerman
2017-10-05 16:17               ` Don Zickus
2017-09-12 19:37 ` [patch V2 23/29] lockup_detector: Get rid of the racy update loop Thomas Gleixner
2017-09-14 10:48   ` [tip:core/urgent] watchdog/core: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 24/29] lockup_detector/perf: Implement init time perf validation Thomas Gleixner
2017-09-14 10:48   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 25/29] lockup_detector: Implement init time detection of perf Thomas Gleixner
2017-09-13 18:02   ` Don Zickus
2017-09-13 18:05     ` Thomas Gleixner
2017-09-14  5:27       ` Ingo Molnar
2017-09-14 10:49   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 26/29] lockup_detector/perf: Implement CPU enable replacement Thomas Gleixner
2017-09-14 10:49   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 27/29] lockup_detector: Use new perf CPU enable mechanism Thomas Gleixner
2017-09-14 10:50   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 28/29] lockup_detector/perf: Simplify deferred event destroy Thomas Gleixner
2017-09-14 10:50   ` [tip:core/urgent] watchdog/hardlockup/perf: " tip-bot for Thomas Gleixner
2017-09-12 19:37 ` [patch V2 29/29] lockup_detector: Cleanup hotplug locking mess Thomas Gleixner
2017-09-14 10:50   ` [tip:core/urgent] watchdog/hardlockup: Clean up " tip-bot for Thomas Gleixner
2017-09-13 18:06 ` [patch V2 00/29] lockup_detector: Cure hotplug deadlocks and replace duct tape Don Zickus
2017-09-14  5:27   ` Ingo Molnar
2017-09-14  8:11   ` Thomas Gleixner

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