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Message-ID: <20231106193524.866104-7-jstultz@google.com>
Date: Mon, 6 Nov 2023 19:34:49 +0000
From: John Stultz <jstultz@...gle.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Joel Fernandes <joelaf@...gle.com>,
Qais Yousef <qyousef@...gle.com>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Valentin Schneider <vschneid@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Zimuzo Ezeozue <zezeozue@...gle.com>,
Youssef Esmat <youssefesmat@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>, kernel-team@...roid.com,
Valentin Schneider <valentin.schneider@....com>,
"Connor O'Brien" <connoro@...gle.com>,
John Stultz <jstultz@...gle.com>
Subject: [PATCH v6 06/20] locking/mutex: Add task_struct::blocked_lock to
serialize changes to the blocked_on state
From: Peter Zijlstra <peterz@...radead.org>
This patch was split out from the later "sched: Add proxy
execution" patch.
Adds blocked_lock to the task_struct so we can safely keep track
of which tasks are blocked on us.
This will be used for tracking blocked-task/mutex chains with
the prox-execution patch in a similar fashion to how priority
inheritence is done with rt_mutexes.
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Qais Yousef <qyousef@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
Cc: Youssef Esmat <youssefesmat@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>
Cc: kernel-team@...roid.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
[rebased, added comments and changelog]
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
[Fixed rebase conflicts]
[squashed sched: Ensure blocked_on is always guarded by blocked_lock]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
[fix rebase conflicts, various fixes & tweaks commented inline]
[squashed sched: Use rq->curr vs rq->proxy checks]
Signed-off-by: Connor O'Brien <connoro@...gle.com>
[jstultz: Split out from bigger patch]
Signed-off-by: John Stultz <jstultz@...gle.com>
---
v2:
* Split out into its own patch
v4:
* Remove verbose comments/questions to avoid review
distractions, as suggested by Dietmar
* Fixed nested block_on locking for ww_mutex access
---
include/linux/sched.h | 1 +
init/init_task.c | 1 +
kernel/fork.c | 1 +
kernel/locking/mutex.c | 24 ++++++++++++++++++++----
kernel/locking/ww_mutex.h | 6 ++++++
5 files changed, 29 insertions(+), 4 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 22a6ac47d5fb..a9258dae00e0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1146,6 +1146,7 @@ struct task_struct {
#endif
struct mutex *blocked_on; /* lock we're blocked on */
+ raw_spinlock_t blocked_lock;
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
int non_block_count;
diff --git a/init/init_task.c b/init/init_task.c
index ff6c4b9bfe6b..189ce67e9704 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -130,6 +130,7 @@ struct task_struct init_task
.journal_info = NULL,
INIT_CPU_TIMERS(init_task)
.pi_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
+ .blocked_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.blocked_lock),
.timer_slack_ns = 50000, /* 50 usec default slack */
.thread_pid = &init_struct_pid,
.thread_group = LIST_HEAD_INIT(init_task.thread_group),
diff --git a/kernel/fork.c b/kernel/fork.c
index 1c3f7eaa9239..47b76ed5ddf6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2353,6 +2353,7 @@ __latent_entropy struct task_struct *copy_process(
ftrace_graph_init_task(p);
rt_mutex_init_task(p);
+ raw_spin_lock_init(&p->blocked_lock);
lockdep_assert_irqs_enabled();
#ifdef CONFIG_PROVE_LOCKING
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 73064e4865b7..df186c0bf4a9 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -592,6 +592,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
}
raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ raw_spin_lock(¤t->blocked_lock);
/*
* After waiting to acquire the wait_lock, try again.
*/
@@ -653,6 +654,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
goto err;
}
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
/* Make sure we do wakeups before calling schedule */
if (!wake_q_empty(&wake_q)) {
@@ -663,6 +665,8 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
first = __mutex_waiter_is_first(lock, &waiter);
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ raw_spin_lock(¤t->blocked_lock);
/*
* Gets reset by unlock path().
*/
@@ -677,15 +681,23 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
break;
if (first) {
+ bool acquired;
+
+ /*
+ * mutex_optimistic_spin() can schedule, so we need to
+ * release these locks before calling it.
+ */
+ raw_spin_unlock(¤t->blocked_lock);
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
- if (mutex_optimistic_spin(lock, ww_ctx, &waiter))
+ acquired = mutex_optimistic_spin(lock, ww_ctx, &waiter);
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ raw_spin_lock(¤t->blocked_lock);
+ if (acquired)
break;
trace_contention_begin(lock, LCB_F_MUTEX);
}
-
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
}
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
acquired:
current->blocked_on = NULL;
__set_current_state(TASK_RUNNING);
@@ -712,6 +724,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
if (ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
preempt_enable();
@@ -724,6 +737,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
err_early_kill:
WARN_ON(current->blocked_on);
trace_contention_end(lock, ret);
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, ip);
@@ -934,8 +948,10 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
next = waiter->task;
debug_mutex_wake_waiter(lock, waiter);
+ raw_spin_lock(&next->blocked_lock);
WARN_ON(next->blocked_on != lock);
next->blocked_on = NULL;
+ raw_spin_unlock(&next->blocked_lock);
wake_q_add(&wake_q, next);
}
diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
index 8bb334491732..2929a95b4272 100644
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -281,6 +281,8 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
return false;
if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) {
+ /* nested as we should hold current->blocked_lock already */
+ raw_spin_lock_nested(&waiter->task->blocked_lock, SINGLE_DEPTH_NESTING);
#ifndef WW_RT
debug_mutex_wake_waiter(lock, waiter);
#endif
@@ -292,6 +294,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
WARN_ON(waiter->task->blocked_on != lock);
waiter->task->blocked_on = NULL;
wake_q_add(wake_q, waiter->task);
+ raw_spin_unlock(&waiter->task->blocked_lock);
}
return true;
@@ -339,6 +342,8 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
* wakeup pending to re-read the wounded state.
*/
if (owner != current) {
+ /* nested as we should hold current->blocked_lock already */
+ raw_spin_lock_nested(&owner->blocked_lock, SINGLE_DEPTH_NESTING);
/*
* When waking up the task to wound, be sure to clear the
* blocked_on pointer. Otherwise we can see circular
@@ -346,6 +351,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
*/
owner->blocked_on = NULL;
wake_q_add(wake_q, owner);
+ raw_spin_unlock(&owner->blocked_lock);
}
return true;
}
--
2.42.0.869.gea05f2083d-goog
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