[patch V4 51/68] locking/rtmutex: Extend the rtmutex core to support ww_mutex

Thomas Gleixner
2021-08-11T12:25:36Z

From: Peter Zijlstra <peterz@infradead.org>

Add a ww acquire context pointer to the waiter and various functions and
add the ww_mutex related invocations to the proper spots in the locking
code similar to the mutex based variant.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: Simplify __waiter_less() (PeterZ)
---
kernel/locking/rtmutex.c | 119 ++++++++++++++++++++++++++++++++++++----
kernel/locking/rtmutex_api.c | 4 -
kernel/locking/rtmutex_common.h | 2
kernel/locking/rwsem.c | 2
4 files changed, 114 insertions(+), 13 deletions(-)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -17,9 +17,44 @@
#include <linux/sched/signal.h>
#include <linux/sched/rt.h>
#include <linux/sched/wake_q.h>
+#include <linux/ww_mutex.h>

#include "rtmutex_common.h"

+#ifndef WW_RT
+# define build_ww_mutex() (false)
+# define ww_container_of(rtm) NULL
+
+static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
+ struct rt_mutex *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ return 0;
+}
+
+static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+}
+
+static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+}
+
+static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
+ struct rt_mutex_waiter *waiter,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ return 0;
+}
+
+#else
+# define build_ww_mutex() (true)
+# define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base)
+# include "ww_mutex.h"
+#endif
+
/*
* lock->owner state tracking:
*
@@ -308,7 +343,28 @@ static __always_inline int rt_mutex_wait

static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
{
- return rt_mutex_waiter_less(__node_2_waiter(a), __node_2_waiter(b));
+ struct rt_mutex_waiter *aw = __node_2_waiter(a);
+ struct rt_mutex_waiter *bw = __node_2_waiter(b);
+
+ if (rt_mutex_waiter_less(aw, bw))
+ return 1;
+
+ if (!build_ww_mutex())
+ return 0;
+
+ if (rt_mutex_waiter_less(bw, aw))
+ return 0;
+
+ /* NOTE: relies on waiter->ww_ctx being set before insertion */
+ if (aw->ww_ctx) {
+ if (!bw->ww_ctx)
+ return 1;
+
+ return (signed long)(aw->ww_ctx->stamp -
+ bw->ww_ctx->stamp) < 0;
+ }
+
+ return 0;
}

static __always_inline void
@@ -961,6 +1017,7 @@ try_to_take_rt_mutex(struct rt_mutex_bas
static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
+ struct ww_acquire_ctx *ww_ctx,
enum rtmutex_chainwalk chwalk)
{
struct task_struct *owner = rt_mutex_owner(lock);
@@ -996,6 +1053,16 @@ static int __sched task_blocks_on_rt_mut

raw_spin_unlock(&task->pi_lock);

+ if (build_ww_mutex() && ww_ctx) {
+ struct rt_mutex *rtm;
+
+ /* Check whether the waiter should backout immediately */
+ rtm = container_of(lock, struct rt_mutex, rtmutex);
+ res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
+ if (res)
+ return res;
+ }
+
if (!owner)
return 0;

@@ -1281,6 +1348,7 @@ static void __sched remove_waiter(struct
/**
* rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
* @lock: the rt_mutex to take
+ * @ww_ctx: WW mutex context pointer
* @state: the state the task should block in (TASK_INTERRUPTIBLE
* or TASK_UNINTERRUPTIBLE)
* @timeout: the pre-initialized and started timer, or NULL for none
@@ -1289,10 +1357,12 @@ static void __sched remove_waiter(struct
* Must be called with lock->wait_lock held and interrupts disabled
*/
static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
+ struct ww_acquire_ctx *ww_ctx,
unsigned int state,
struct hrtimer_sleeper *timeout,
struct rt_mutex_waiter *waiter)
{
+ struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
int ret = 0;

for (;;) {
@@ -1309,6 +1379,12 @@ static int __sched rt_mutex_slowlock_blo
break;
}

+ if (build_ww_mutex() && ww_ctx) {
+ ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
+ if (ret)
+ break;
+ }
+
raw_spin_unlock_irq(&lock->wait_lock);

schedule();
@@ -1331,6 +1407,9 @@ static void __sched rt_mutex_handle_dead
if (res != -EDEADLOCK || detect_deadlock)
return;

+ if (build_ww_mutex() && w->ww_ctx)
+ return;
+
/*
* Yell loudly and stop the task right here.
*/
@@ -1344,31 +1423,46 @@ static void __sched rt_mutex_handle_dead
/**
* __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
* @lock: The rtmutex to block lock
+ * @ww_ctx: WW mutex context pointer
* @state: The task state for sleeping
* @chwalk: Indicator whether full or partial chainwalk is requested
* @waiter: Initializer waiter for blocking
*/
static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
+ struct ww_acquire_ctx *ww_ctx,
unsigned int state,
enum rtmutex_chainwalk chwalk,
struct rt_mutex_waiter *waiter)
{
+ struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
+ struct ww_mutex *ww = ww_container_of(rtm);
int ret;

lockdep_assert_held(&lock->wait_lock);

/* Try to acquire the lock again: */
- if (try_to_take_rt_mutex(lock, current, NULL))
+ if (try_to_take_rt_mutex(lock, current, NULL)) {
+ if (build_ww_mutex() && ww_ctx) {
+ __ww_mutex_check_waiters(rtm, ww_ctx);
+ ww_mutex_lock_acquired(ww, ww_ctx);
+ }
return 0;
+ }

set_current_state(state);

- ret = task_blocks_on_rt_mutex(lock, waiter, current, chwalk);
-
+ ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
if (likely(!ret))
- ret = rt_mutex_slowlock_block(lock, state, NULL, waiter);
+ ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);

- if (unlikely(ret)) {
+ if (likely(!ret)) {
+ /* acquired the lock */
+ if (build_ww_mutex() && ww_ctx) {
+ if (!ww_ctx->is_wait_die)
+ __ww_mutex_check_waiters(rtm, ww_ctx);
+ ww_mutex_lock_acquired(ww, ww_ctx);
+ }
+ } else {
__set_current_state(TASK_RUNNING);
remove_waiter(lock, waiter);
rt_mutex_handle_deadlock(ret, chwalk, waiter);
@@ -1383,14 +1477,17 @@ static int __sched __rt_mutex_slowlock(s
}

static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
+ struct ww_acquire_ctx *ww_ctx,
unsigned int state)
{
struct rt_mutex_waiter waiter;
int ret;

rt_mutex_init_waiter(&waiter);
+ waiter.ww_ctx = ww_ctx;

- ret = __rt_mutex_slowlock(lock, state, RT_MUTEX_MIN_CHAINWALK, &waiter);
+ ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
+ &waiter);

debug_rt_mutex_free_waiter(&waiter);
return ret;
@@ -1399,9 +1496,11 @@ static inline int __rt_mutex_slowlock_lo
/*
* rt_mutex_slowlock - Locking slowpath invoked when fast path fails
* @lock: The rtmutex to block lock
+ * @ww_ctx: WW mutex context pointer
* @state: The task state for sleeping
*/
static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
+ struct ww_acquire_ctx *ww_ctx,
unsigned int state)
{
unsigned long flags;
@@ -1416,7 +1515,7 @@ static int __sched rt_mutex_slowlock(str
* irqsave/restore variants.
*/
raw_spin_lock_irqsave(&lock->wait_lock, flags);
- ret = __rt_mutex_slowlock_locked(lock, state);
+ ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

return ret;
@@ -1428,7 +1527,7 @@ static __always_inline int __rt_mutex_lo
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
return 0;

- return rt_mutex_slowlock(lock, state);
+ return rt_mutex_slowlock(lock, NULL, state);
}
#endif /* RT_MUTEX_BUILD_MUTEX */

@@ -1455,7 +1554,7 @@ static void __sched rtlock_slowlock_lock
/* Save current state and set state to TASK_RTLOCK_WAIT */
current_save_and_set_rtlock_wait_state();

- task_blocks_on_rt_mutex(lock, &waiter, current, RT_MUTEX_MIN_CHAINWALK);
+ task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);

for (;;) {
/* Try to acquire the lock again. */
--- a/kernel/locking/rtmutex_api.c
+++ b/kernel/locking/rtmutex_api.c
@@ -267,7 +267,7 @@ int __sched __rt_mutex_start_proxy_lock(
return 1;

/* We enforce deadlock detection for futexes */
- ret = task_blocks_on_rt_mutex(lock, waiter, task,
+ ret = task_blocks_on_rt_mutex(lock, waiter, task, NULL,
RT_MUTEX_FULL_CHAINWALK);

if (ret && !rt_mutex_owner(lock)) {
@@ -343,7 +343,7 @@ int __sched rt_mutex_wait_proxy_lock(str
raw_spin_lock_irq(&lock->wait_lock);
/* sleep on the mutex */
set_current_state(TASK_INTERRUPTIBLE);
- ret = rt_mutex_slowlock_block(lock, TASK_INTERRUPTIBLE, to, waiter);
+ ret = rt_mutex_slowlock_block(lock, NULL, TASK_INTERRUPTIBLE, to, waiter);
/*
* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
* have to fix that up.
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -28,6 +28,7 @@
* @wake_state: Wakeup state to use (TASK_NORMAL or TASK_RTLOCK_WAIT)
* @prio: Priority of the waiter
* @deadline: Deadline of the waiter if applicable
+ * @ww_ctx: WW context pointer
*/
struct rt_mutex_waiter {
struct rb_node tree_entry;
@@ -37,6 +38,7 @@ struct rt_mutex_waiter {
unsigned int wake_state;
int prio;
u64 deadline;
+ struct ww_acquire_ctx *ww_ctx;
};

/**
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1360,7 +1360,7 @@ static inline void __downgrade_write(str
__rt_mutex_lock(rtm, state)

#define rwbase_rtmutex_slowlock_locked(rtm, state) \
- __rt_mutex_slowlock_locked(rtm, state)
+ __rt_mutex_slowlock_locked(rtm, NULL, state)

#define rwbase_rtmutex_unlock(rtm) \
__rt_mutex_unlock(rtm)