rtmutex: Cleanup deadlock detector debug logic
The conditions under which deadlock detection is conducted are unclear
and undocumented.
Add constants instead of using 0/1 and provide a selection function
which hides the additional debug dependency from the calling code.
Add comments where needed.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Link: http://lkml.kernel.org/r/20140522031949.947264874@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 3290648..c6ffdaa 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -308,6 +308,32 @@
}
/*
+ * Deadlock detection is conditional:
+ *
+ * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
+ * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
+ *
+ * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
+ * conducted independent of the detect argument.
+ *
+ * If the waiter argument is NULL this indicates the deboost path and
+ * deadlock detection is disabled independent of the detect argument
+ * and the config settings.
+ */
+static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
+ enum rtmutex_chainwalk chwalk)
+{
+ /*
+ * This is just a wrapper function for the following call,
+ * because debug_rt_mutex_detect_deadlock() smells like a magic
+ * debug feature and I wanted to keep the cond function in the
+ * main source file along with the comments instead of having
+ * two of the same in the headers.
+ */
+ return debug_rt_mutex_detect_deadlock(waiter, chwalk);
+}
+
+/*
* Max number of times we'll walk the boosting chain:
*/
int max_lock_depth = 1024;
@@ -381,7 +407,7 @@
* goto again;
*/
static int rt_mutex_adjust_prio_chain(struct task_struct *task,
- int deadlock_detect,
+ enum rtmutex_chainwalk chwalk,
struct rt_mutex *orig_lock,
struct rt_mutex *next_lock,
struct rt_mutex_waiter *orig_waiter,
@@ -389,12 +415,12 @@
{
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
struct rt_mutex_waiter *prerequeue_top_waiter;
- int detect_deadlock, ret = 0, depth = 0;
+ int ret = 0, depth = 0;
struct rt_mutex *lock;
+ bool detect_deadlock;
unsigned long flags;
- detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
- deadlock_detect);
+ detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
/*
* The (de)boosting is a step by step approach with a lot of
@@ -520,7 +546,7 @@
* walk, we detected a deadlock.
*/
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
- debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
+ debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
raw_spin_unlock(&lock->wait_lock);
ret = -EDEADLK;
goto out_unlock_pi;
@@ -784,7 +810,7 @@
static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
- int detect_deadlock)
+ enum rtmutex_chainwalk chwalk)
{
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex_waiter *top_waiter = waiter;
@@ -830,7 +856,7 @@
__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on)
chain_walk = 1;
- } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
+ } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
chain_walk = 1;
}
@@ -855,7 +881,7 @@
raw_spin_unlock(&lock->wait_lock);
- res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
+ res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
next_lock, waiter, task);
raw_spin_lock(&lock->wait_lock);
@@ -960,7 +986,8 @@
raw_spin_unlock(&lock->wait_lock);
- rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
+ rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
+ next_lock, NULL, current);
raw_spin_lock(&lock->wait_lock);
}
@@ -990,7 +1017,8 @@
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(task);
- rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
+ rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
+ next_lock, NULL, task);
}
/**
@@ -1068,7 +1096,7 @@
static int __sched
rt_mutex_slowlock(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
- int detect_deadlock)
+ enum rtmutex_chainwalk chwalk)
{
struct rt_mutex_waiter waiter;
int ret = 0;
@@ -1094,7 +1122,7 @@
timeout->task = NULL;
}
- ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
+ ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
if (likely(!ret))
ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
@@ -1103,7 +1131,7 @@
if (unlikely(ret)) {
remove_waiter(lock, &waiter);
- rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
+ rt_mutex_handle_deadlock(ret, chwalk, &waiter);
}
/*
@@ -1230,27 +1258,29 @@
rt_mutex_fastlock(struct rt_mutex *lock, int state,
int (*slowfn)(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
- int detect_deadlock))
+ enum rtmutex_chainwalk chwalk))
{
if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
rt_mutex_deadlock_account_lock(lock, current);
return 0;
} else
- return slowfn(lock, state, NULL, 0);
+ return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
}
static inline int
rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
- struct hrtimer_sleeper *timeout, int detect_deadlock,
+ struct hrtimer_sleeper *timeout,
+ enum rtmutex_chainwalk chwalk,
int (*slowfn)(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
- int detect_deadlock))
+ enum rtmutex_chainwalk chwalk))
{
- if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
+ if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
+ likely(rt_mutex_cmpxchg(lock, NULL, current))) {
rt_mutex_deadlock_account_lock(lock, current);
return 0;
} else
- return slowfn(lock, state, timeout, detect_deadlock);
+ return slowfn(lock, state, timeout, chwalk);
}
static inline int
@@ -1312,7 +1342,8 @@
{
might_sleep();
- return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout, 1,
+ return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+ RT_MUTEX_FULL_CHAINWALK,
rt_mutex_slowlock);
}
@@ -1334,7 +1365,8 @@
{
might_sleep();
- return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout, 0,
+ return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+ RT_MUTEX_MIN_CHAINWALK,
rt_mutex_slowlock);
}
EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
@@ -1463,7 +1495,8 @@
}
/* We enforce deadlock detection for futexes */
- ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
+ ret = task_blocks_on_rt_mutex(lock, waiter, task,
+ RT_MUTEX_FULL_CHAINWALK);
if (ret && !rt_mutex_owner(lock)) {
/*