[patch V2 03/15] locking/rtmutex: Remove output from deadlock detector.

From: Thomas Gleixner
Date: Fri Mar 26 2021 - 12:02:28 EST

From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

The rtmutex specific deadlock detector predates lockdep coverage of rtmutex
and since commit f5694788ad8da ("rt_mutex: Add lockdep annotations") it
contains a lot of redundant functionality.

- lockdep will detect an potential deadlock before rtmutex-debug
has a chance to do so

- the dead lock debugging is restricted to rtmutexes which are not
associated to futexes and have an active waiter, which is covered by
lockdep already

Remove the redundant functionality and move actual deadlock WARN() into the
deadlock code path. The latter needs a seperate cleanup.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
include/linux/rtmutex.h | 7 --
kernel/locking/rtmutex-debug.c | 97 ----------------------------------------
kernel/locking/rtmutex-debug.h | 9 ---
kernel/locking/rtmutex.c | 7 --
kernel/locking/rtmutex.h | 7 --
kernel/locking/rtmutex_common.h | 4 -
6 files changed, 1 insertion(+), 130 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
@@ -18,18 +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);

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
@@ -579,7 +579,6 @@ 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;
@@ -1171,8 +1170,6 @@ static int __sched

raw_spin_unlock_irq(&lock->wait_lock);

- debug_rt_mutex_print_deadlock(waiter);
-
schedule();

raw_spin_lock_irq(&lock->wait_lock);
@@ -1196,7 +1193,7 @@ static void rt_mutex_handle_deadlock(int
/*
* Yell loudly and stop the task right here.
*/
- rt_mutex_print_deadlock(w);
+ WARN(1, "rtmutex deadlock detected\n");
while (1) {
set_current_state(TASK_INTERRUPTIBLE);
schedule();
@@ -1704,8 +1701,6 @@ 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
@@ -18,13 +18,6 @@
#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)
-
-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;
};