[RFC][PATCH] locking: Debug nested wait/locking primitives

Peter Zijlstra
2014-08-02T20:04:51Z

This should cover most cases I think.

I'll have to break this out into different patches, and maybe clean up
things a bit (there's certainly comments missing and some repetition).

But this boots on my test box and builds a kernel without generating a
single WARN -- big improvement over not booting (partly due to excessive
warn output) with just the sched/core.c bit.

---
drivers/tty/n_tty.c | 71 +++++++++++++++++++++++++++++++++-------
fs/notify/inotify/inotify_user.c | 34 +++++++++++++++++--
fs/notify/notification.c | 2 +-
include/linux/kernel.h | 4 +--
include/linux/sched.h | 46 ++++++++++++++++++++++++--
include/linux/wait.h | 2 ++
kernel/exit.c | 6 ++++
kernel/sched/core.c | 14 ++++++++
kernel/smpboot.c | 15 +++++----
9 files changed, 168 insertions(+), 26 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index f44f1ba762c3..5e4830979937 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2098,6 +2098,36 @@ static int job_control(struct tty_struct *tty, struct file *file)
return 0;
}

+/*
+ * n_tty_{read,write} use blocking primitives (mutex_lock, down_read, etc.)
+ * inside an open-coded wait loop.
+ *
+ * The wait loop relies on current->state to record wakeups; these will change
+ * it back to TASK_RUNNING. However blocking primitives themselves also change
+ * current->state. Therefore we must implement another means of recording
+ * wakeups.
+ *
+ * We do this by setting an alternative waitqueue wake function which changes
+ * an additional variable.
+ */
+
+struct n_tty_wakeup_state {
+ struct task_struct *task;
+ bool woken;
+};
+
+static int n_tty_wake(wait_queue_t *wait, unsigned mode,
+ int wake_flags, void *key)
+{
+ struct n_tty_wakeup_state *s = wait->private;
+ DECLARE_WAITQUEUE(dummy_wait, s->task);
+
+ smp_wmb();
+ s->woken = true;
+
+ return default_wake_function(&dummy_wait, mode, wake_flags, key);
+}
+

/**
* n_tty_read - read function for tty
@@ -2123,7 +2153,11 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
{
struct n_tty_data *ldata = tty->disc_data;
unsigned char __user *b = buf;
- DECLARE_WAITQUEUE(wait, current);
+ struct n_tty_wakeup_state s = {
+ .task = current,
+ .woken = false,
+ };
+ wait_queue_t wait;
int c;
int minimum, time;
ssize_t retval = 0;
@@ -2167,6 +2201,9 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,

packet = tty->packet;

+ init_waitqueue_func_entry(&wait, n_tty_wake);
+ wait.private = &s;
+
add_wait_queue(&tty->read_wait, &wait);
while (nr) {
/* First test for status change. */
@@ -2186,10 +2223,11 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
nr--;
break;
}
- /* This statement must be first before checking for input
- so that any interrupt will set the state back to
- TASK_RUNNING. */
- set_current_state(TASK_INTERRUPTIBLE);
+ /*
+ * This statement must be first before checking for input so
+ * that any interrupt will set it to true.
+ */
+ s.woken = false;

if (((minimum - (b - buf)) < ldata->minimum_to_wake) &&
((minimum - (b - buf)) >= 1))
@@ -2220,13 +2258,15 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
n_tty_set_room(tty);
up_read(&tty->termios_rwsem);

- timeout = schedule_timeout(timeout);
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (!s.woken)
+ timeout = schedule_timeout(timeout);
+ __set_current_state(TASK_RUNNING);

down_read(&tty->termios_rwsem);
continue;
}
}
- __set_current_state(TASK_RUNNING);

/* Deal with packet mode. */
if (packet && b == buf) {
@@ -2273,7 +2313,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,

mutex_unlock(&ldata->atomic_read_lock);

- __set_current_state(TASK_RUNNING);
if (b - buf)
retval = b - buf;

@@ -2306,7 +2345,11 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t nr)
{
const unsigned char *b = buf;
- DECLARE_WAITQUEUE(wait, current);
+ struct n_tty_wakeup_state s = {
+ .task = current,
+ .woken = false,
+ };
+ wait_queue_t wait;
int c;
ssize_t retval = 0;

@@ -2322,9 +2365,12 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
/* Write out any echoed characters that are still pending */
process_echoes(tty);

+ init_waitqueue_func_entry(&wait, n_tty_wake);
+ wait.private = &s;
+
add_wait_queue(&tty->write_wait, &wait);
while (1) {
- set_current_state(TASK_INTERRUPTIBLE);
+ s.woken = false;
if (signal_pending(current)) {
retval = -ERESTARTSYS;
break;
@@ -2378,7 +2424,10 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
}
up_read(&tty->termios_rwsem);

- schedule();
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (!s.woken)
+ schedule();
+ __set_current_state(TASK_RUNNING);

down_read(&tty->termios_rwsem);
}
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index cc423a30a0c8..e3b65ce6b312 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -220,6 +220,23 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
return event_size;
}

+struct inotify_wakeup_state {
+ struct task_struct *task;
+ bool woken;
+};
+
+static int inotify_wake(wait_queue_t *wait, unsigned mode,
+ int wake_flags, void *key)
+{
+ struct inotify_wakeup_state *s = wait->private;
+ DECLARE_WAITQUEUE(dummy_wait, s->task);
+
+ smp_wmb();
+ s->woken = true;
+
+ return autoremove_wake_function(&dummy_wait, mode, wake_flags, key);
+}
+
static ssize_t inotify_read(struct file *file, char __user *buf,
size_t count, loff_t *pos)
{
@@ -227,13 +244,21 @@ static ssize_t inotify_read(struct file *file, char __user *buf,
struct fsnotify_event *kevent;
char __user *start;
int ret;
- DEFINE_WAIT(wait);
+ struct inotify_wakeup_state s = {
+ .task = current,
+ .woken = false,
+ };
+ wait_queue_t wait;
+
+ init_waitqueue_func_entry(&wait, inotify_wake);
+ wait.private = &s;

start = buf;
group = file->private_data;

+ add_wait_queue(&group->notification_waitq, &wait);
while (1) {
- prepare_to_wait(&group->notification_waitq, &wait, TASK_INTERRUPTIBLE);
+ s.woken = false;

mutex_lock(&group->notification_mutex);
kevent = get_one_event(group, count);
@@ -264,7 +289,10 @@ static ssize_t inotify_read(struct file *file, char __user *buf,
if (start != buf)
break;

- schedule();
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (!s.woken)
+ schedule();
+ __set_current_state(TASK_RUNNING);
}

finish_wait(&group->notification_waitq, &wait);
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 1e58402171a5..dcfcdd69d1de 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -63,7 +63,7 @@ EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
/* return true if the notify queue is empty, false otherwise */
bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group)
{
- BUG_ON(!mutex_is_locked(&group->notification_mutex));
+ lockdep_assert_held(&group->notification_mutex);
return list_empty(&group->notification_list) ? true : false;
}

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4c52907a6d8b..aac1dc9da2d0 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -162,7 +162,7 @@ extern int _cond_resched(void);
#endif

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
- void __might_sleep(const char *file, int line, int preempt_offset);
+extern void __might_sleep(const char *file, int line, int preempt_offset);
/**
* might_sleep - annotation for functions that can sleep
*
@@ -174,7 +174,7 @@ extern int _cond_resched(void);
* supposed to.
*/
# define might_sleep() \
- do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
+ do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
#else
static inline void __might_sleep(const char *file, int line,
int preempt_offset) { }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 66124d63371a..62dab5738e66 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -241,6 +241,43 @@ extern char ___assert_task_state[1 - 2*!!(
((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
(task->flags & PF_FROZEN) == 0)

+#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
+
+#define __set_task_state(tsk, state_value) \
+ do { \
+ (tsk)->task_state_change = _THIS_IP_; \
+ (tsk)->state = (state_value); \
+ } while (0)
+#define set_task_state(tsk, state_value) \
+ do { \
+ (tsk)->task_state_change = _THIS_IP_; \
+ set_mb((tsk)->state, (state_value)); \
+ } while (0)
+
+/*
+ * set_current_state() includes a barrier so that the write of current->state
+ * is correctly serialised wrt the caller's subsequent test of whether to
+ * actually sleep:
+ *
+ * set_current_state(TASK_UNINTERRUPTIBLE);
+ * if (do_i_need_to_sleep())
+ * schedule();
+ *
+ * If the caller does not need such serialisation then use __set_current_state()
+ */
+#define __set_current_state(state_value) \
+ do { \
+ current->task_state_change = _THIS_IP_; \
+ current->state = (state_value); \
+ } while (0)
+#define set_current_state(state_value) \
+ do { \
+ current->task_state_change = _THIS_IP_; \
+ set_mb(current->state, (state_value)); \
+ } while (0)
+
+#else
+
#define __set_task_state(tsk, state_value) \
do { (tsk)->state = (state_value); } while (0)
#define set_task_state(tsk, state_value) \
@@ -257,11 +294,13 @@ extern char ___assert_task_state[1 - 2*!!(
*
* If the caller does not need such serialisation then use __set_current_state()
*/
-#define __set_current_state(state_value) \
+#define __set_current_state(state_value) \
do { current->state = (state_value); } while (0)
-#define set_current_state(state_value) \
+#define set_current_state(state_value) \
set_mb(current->state, (state_value))

+#endif
+
/* Task command name length */
#define TASK_COMM_LEN 16

@@ -1650,6 +1689,9 @@ struct task_struct {
unsigned int sequential_io;
unsigned int sequential_io_avg;
#endif
+#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
+ unsigned long task_state_change;
+#endif
};

/* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 6fb1ba5f9b2f..041b744e99b4 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -211,6 +211,8 @@ wait_queue_head_t *bit_waitqueue(void *, int);
wait_queue_t __wait; \
long __ret = ret; /* explicit shadow */ \
\
+ might_sleep(); \
+ \
INIT_LIST_HEAD(&__wait.task_list); \
if (exclusive) \
__wait.flags = WQ_FLAG_EXCLUSIVE; \
diff --git a/kernel/exit.c b/kernel/exit.c
index e5c4668f1799..44cbc8791fca 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1067,6 +1067,12 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
}

/*
+ * Since we're going to terminate the wait loop from do_wait(),
+ * reset task state.
+ */
+ __set_current_state(TASK_RUNNING);
+
+ /*
* Now we are sure this task is interesting, and no other
* thread can reap it because we its state == DEAD/TRACE.
*/
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2676866b4394..0577c12c9cf8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7077,6 +7077,19 @@ void __might_sleep(const char *file, int line, int preempt_offset)
{
static unsigned long prev_jiffy; /* ratelimiting */

+ /*
+ * Blocking primitives will set (and therefore destroy) current->state,
+ * since we will exit with TASK_RUNNING make sure we enter with it,
+ * otherwise we will destroy state.
+ */
+ if (WARN(current->state != TASK_RUNNING,
+ "do not call blocking ops when !TASK_RUNNING; "
+ "state=%lx set at [<%p>] %pS\n",
+ current->state,
+ current->task_state_change,
+ current->task_state_change))
+ __set_current_state(TASK_RUNNING);
+
rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
!is_idle_task(current)) ||
@@ -7107,6 +7120,7 @@ void __might_sleep(const char *file, int line, int preempt_offset)
dump_stack();
}
EXPORT_SYMBOL(__might_sleep);
+
#endif

#ifdef CONFIG_MAGIC_SYSRQ
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index eb89e1807408..f032fb5284e3 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -110,7 +110,7 @@ static int smpboot_thread_fn(void *data)
set_current_state(TASK_INTERRUPTIBLE);
preempt_disable();
if (kthread_should_stop()) {
- set_current_state(TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
preempt_enable();
if (ht->cleanup)
ht->cleanup(td->cpu, cpu_online(td->cpu));
@@ -136,26 +136,27 @@ static int smpboot_thread_fn(void *data)
/* Check for state change setup */
switch (td->status) {
case HP_THREAD_NONE:
+ __set_current_state(TASK_RUNNING);
preempt_enable();
if (ht->setup)
ht->setup(td->cpu);
td->status = HP_THREAD_ACTIVE;
- preempt_disable();
- break;
+ continue;
+
case HP_THREAD_PARKED:
+ __set_current_state(TASK_RUNNING);
preempt_enable();
if (ht->unpark)
ht->unpark(td->cpu);
td->status = HP_THREAD_ACTIVE;
- preempt_disable();
- break;
+ continue;
}

if (!ht->thread_should_run(td->cpu)) {
- preempt_enable();
+ preempt_enable_no_resched();
schedule();
} else {
- set_current_state(TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
preempt_enable();
ht->thread_fn(td->cpu);
}