path: root/patches/0002-locking-rtmutex-Remove-output-from-deadlock-detector.patch

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 29 Sep 2020 16:05:11 +0200
Subject: [PATCH 02/23] locking/rtmutex: Remove output from deadlock detector.

In commit
  f5694788ad8da ("rt_mutex: Add lockdep annotations")

rtmutex gained lockdep annotation for rt_mutex_lock() and and related
functions.
lockdep will see the locking order and may complain about a deadlock
before rtmutex' own mechanism gets a chance to detect it.
The rtmutex deadlock detector will only complain locks with the
RT_MUTEX_MIN_CHAINWALK and a waiter must be pending. That means it
works only for in-kernel locks because the futex interface always uses
RT_MUTEX_FULL_CHAINWALK.
The requirement for an active waiter limits the detector to actual
deadlocks and makes it possible to report potential deadlocks like
lockdep does.
It looks like lockdep is better suited for reporting deadlocks.

Remove rtmutex' debug print on deadlock detection.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/rtmutex.h         |    7 --
 kernel/locking/rtmutex-debug.c  |   97 ----------------------------------------
 kernel/locking/rtmutex-debug.h  |   11 ----
 kernel/locking/rtmutex.c        |    9 ---
 kernel/locking/rtmutex.h        |    7 --
 kernel/locking/rtmutex_common.h |    4 -
 6 files changed, 135 deletions(-)

--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -31,9 +31,6 @@ struct rt_mutex {
 	raw_spinlock_t		wait_lock;
 	struct rb_root_cached   waiters;
 	struct task_struct	*owner;
-#ifdef CONFIG_DEBUG_RT_MUTEXES
-	const char		*name;
-#endif
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
@@ -56,8 +53,6 @@ struct hrtimer_sleeper;
 #endif
 
 #ifdef CONFIG_DEBUG_RT_MUTEXES
-# define __DEBUG_RT_MUTEX_INITIALIZER(mutexname) \
-	, .name = #mutexname
 
 # define rt_mutex_init(mutex) \
 do { \
@@ -67,7 +62,6 @@ do { \
 
  extern void rt_mutex_debug_task_free(struct task_struct *tsk);
 #else
-# define __DEBUG_RT_MUTEX_INITIALIZER(mutexname)
 # define rt_mutex_init(mutex)			__rt_mutex_init(mutex, NULL, NULL)
 # define rt_mutex_debug_task_free(t)			do { } while (0)
 #endif
@@ -83,7 +77,6 @@ do { \
 	{ .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(mutexname.wait_lock) \
 	, .waiters = RB_ROOT_CACHED \
 	, .owner = NULL \
-	__DEBUG_RT_MUTEX_INITIALIZER(mutexname) \
 	__DEP_MAP_RT_MUTEX_INITIALIZER(mutexname)}
 
 #define DEFINE_RT_MUTEX(mutexname) \
--- a/kernel/locking/rtmutex-debug.c
+++ b/kernel/locking/rtmutex-debug.c
@@ -32,105 +32,12 @@
 
 #include "rtmutex_common.h"
 
-static void printk_task(struct task_struct *p)
-{
-	if (p)
-		printk("%16s:%5d [%p, %3d]", p->comm, task_pid_nr(p), p, p->prio);
-	else
-		printk("<none>");
-}
-
-static void printk_lock(struct rt_mutex *lock, int print_owner)
-{
-	printk(" [%p] {%s}\n", lock, lock->name);
-
-	if (print_owner && rt_mutex_owner(lock)) {
-		printk(".. ->owner: %p\n", lock->owner);
-		printk(".. held by:  ");
-		printk_task(rt_mutex_owner(lock));
-		printk("\n");
-	}
-}
-
 void rt_mutex_debug_task_free(struct task_struct *task)
 {
 	DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters.rb_root));
 	DEBUG_LOCKS_WARN_ON(task->pi_blocked_on);
 }
 
-/*
- * We fill out the fields in the waiter to store the information about
- * the deadlock. We print when we return. act_waiter can be NULL in
- * case of a remove waiter operation.
- */
-void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
-			     struct rt_mutex_waiter *act_waiter,
-			     struct rt_mutex *lock)
-{
-	struct task_struct *task;
-
-	if (!debug_locks || chwalk == RT_MUTEX_FULL_CHAINWALK || !act_waiter)
-		return;
-
-	task = rt_mutex_owner(act_waiter->lock);
-	if (task && task != current) {
-		act_waiter->deadlock_task_pid = get_pid(task_pid(task));
-		act_waiter->deadlock_lock = lock;
-	}
-}
-
-void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter)
-{
-	struct task_struct *task;
-
-	if (!waiter->deadlock_lock || !debug_locks)
-		return;
-
-	rcu_read_lock();
-	task = pid_task(waiter->deadlock_task_pid, PIDTYPE_PID);
-	if (!task) {
-		rcu_read_unlock();
-		return;
-	}
-
-	if (!debug_locks_off()) {
-		rcu_read_unlock();
-		return;
-	}
-
-	pr_warn("\n");
-	pr_warn("============================================\n");
-	pr_warn("WARNING: circular locking deadlock detected!\n");
-	pr_warn("%s\n", print_tainted());
-	pr_warn("--------------------------------------------\n");
-	printk("%s/%d is deadlocking current task %s/%d\n\n",
-	       task->comm, task_pid_nr(task),
-	       current->comm, task_pid_nr(current));
-
-	printk("\n1) %s/%d is trying to acquire this lock:\n",
-	       current->comm, task_pid_nr(current));
-	printk_lock(waiter->lock, 1);
-
-	printk("\n2) %s/%d is blocked on this lock:\n",
-		task->comm, task_pid_nr(task));
-	printk_lock(waiter->deadlock_lock, 1);
-
-	debug_show_held_locks(current);
-	debug_show_held_locks(task);
-
-	printk("\n%s/%d's [blocked] stackdump:\n\n",
-		task->comm, task_pid_nr(task));
-	show_stack(task, NULL, KERN_DEFAULT);
-	printk("\n%s/%d's [current] stackdump:\n\n",
-		current->comm, task_pid_nr(current));
-	dump_stack();
-	debug_show_all_locks();
-	rcu_read_unlock();
-
-	printk("[ turning off deadlock detection."
-	       "Please report this trace. ]\n\n");
-}
-
 void debug_rt_mutex_lock(struct rt_mutex *lock)
 {
 }
@@ -153,12 +60,10 @@ void debug_rt_mutex_proxy_unlock(struct
 void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
 {
 	memset(waiter, 0x11, sizeof(*waiter));
-	waiter->deadlock_task_pid = NULL;
 }
 
 void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
 {
-	put_pid(waiter->deadlock_task_pid);
 	memset(waiter, 0x22, sizeof(*waiter));
 }
 
@@ -168,10 +73,8 @@ void debug_rt_mutex_init(struct rt_mutex
 	 * Make sure we are not reinitializing a held lock:
 	 */
 	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
-	lock->name = name;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	lockdep_init_map(&lock->dep_map, name, key, 0);
 #endif
 }
-
--- a/kernel/locking/rtmutex-debug.h
+++ b/kernel/locking/rtmutex-debug.h
@@ -18,20 +18,9 @@ extern void debug_rt_mutex_unlock(struct
 extern void debug_rt_mutex_proxy_lock(struct rt_mutex *lock,
 				      struct task_struct *powner);
 extern void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock);
-extern void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
-				    struct rt_mutex_waiter *waiter,
-				    struct rt_mutex *lock);
-extern void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter);
-# define debug_rt_mutex_reset_waiter(w)			\
-	do { (w)->deadlock_lock = NULL; } while (0)
 
 static inline bool debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter,
 						  enum rtmutex_chainwalk walk)
 {
 	return (waiter != NULL);
 }
-
-static inline void rt_mutex_print_deadlock(struct rt_mutex_waiter *w)
-{
-	debug_rt_mutex_print_deadlock(w);
-}
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -597,7 +597,6 @@ static int rt_mutex_adjust_prio_chain(st
 	 * walk, we detected a deadlock.
 	 */
 	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
-		debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
 		raw_spin_unlock(&lock->wait_lock);
 		ret = -EDEADLK;
 		goto out_unlock_pi;
@@ -1189,8 +1188,6 @@ static int __sched
 
 		raw_spin_unlock_irq(&lock->wait_lock);
 
-		debug_rt_mutex_print_deadlock(waiter);
-
 		schedule();
 
 		raw_spin_lock_irq(&lock->wait_lock);
@@ -1211,10 +1208,6 @@ static void rt_mutex_handle_deadlock(int
 	if (res != -EDEADLOCK || detect_deadlock)
 		return;
 
-	/*
-	 * Yell lowdly and stop the task right here.
-	 */
-	rt_mutex_print_deadlock(w);
 	while (1) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		schedule();
@@ -1764,8 +1757,6 @@ int __rt_mutex_start_proxy_lock(struct r
 		ret = 0;
 	}
 
-	debug_rt_mutex_print_deadlock(waiter);
-
 	return ret;
 }
 
--- a/kernel/locking/rtmutex.h
+++ b/kernel/locking/rtmutex.h
@@ -19,15 +19,8 @@
 #define debug_rt_mutex_proxy_unlock(l)			do { } while (0)
 #define debug_rt_mutex_unlock(l)			do { } while (0)
 #define debug_rt_mutex_init(m, n, k)			do { } while (0)
-#define debug_rt_mutex_deadlock(d, a ,l)		do { } while (0)
-#define debug_rt_mutex_print_deadlock(w)		do { } while (0)
 #define debug_rt_mutex_reset_waiter(w)			do { } while (0)
 
-static inline void rt_mutex_print_deadlock(struct rt_mutex_waiter *w)
-{
-	WARN(1, "rtmutex deadlock detected\n");
-}
-
 static inline bool debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *w,
 						  enum rtmutex_chainwalk walk)
 {
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -29,10 +29,6 @@ struct rt_mutex_waiter {
 	struct rb_node          pi_tree_entry;
 	struct task_struct	*task;
 	struct rt_mutex		*lock;
-#ifdef CONFIG_DEBUG_RT_MUTEXES
-	struct pid		*deadlock_task_pid;
-	struct rt_mutex		*deadlock_lock;
-#endif
 	int prio;
 	u64 deadline;
 };