150 lines
4.7 KiB
Diff
150 lines
4.7 KiB
Diff
From a1ea4ba483d5fde2145878a8e797cf8b7a81538d Mon Sep 17 00:00:00 2001
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Thu, 22 Jun 2017 17:53:34 +0200
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Subject: [PATCH 176/365] kernel/locking: use an exclusive wait_q for sleepers
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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If a task is queued as a sleeper for a wakeup and never goes to
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schedule() (because it just obtained the lock) then it will receive a
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spurious wake up which is not "bad", it is considered. Until that wake
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up happens this task can no be enqueued for any wake ups handled by the
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WAKE_Q infrastructure (because a task can only be enqueued once). This
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wouldn't be bad if we would use the same wakeup mechanism for the wake
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up of sleepers as we do for "normal" wake ups. But we don't…
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So.
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T1 T2 T3
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spin_lock(x) spin_unlock(x);
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wake_q_add_sleeper(q1, T1)
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spin_unlock(x)
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set_state(TASK_INTERRUPTIBLE)
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if (!condition)
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schedule()
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condition = true
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wake_q_add(q2, T1)
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// T1 not added, still enqueued
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wake_up_q(q2)
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wake_up_q_sleeper(q1)
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// T1 not woken up, wrong task state
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In order to solve this race this patch adds a wake_q_node for the
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sleeper case.
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Reported-by: Mike Galbraith <efault@gmx.de>
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Cc: stable-rt@vger.kernel.org
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/sched.h | 17 +++++++++++++++--
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kernel/fork.c | 1 +
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kernel/locking/rtmutex.c | 2 +-
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kernel/sched/core.c | 20 ++++++++++++++++----
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4 files changed, 33 insertions(+), 7 deletions(-)
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diff --git a/include/linux/sched.h b/include/linux/sched.h
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index 9b7c9209e8ea..364ec7e0b38d 100644
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--- a/include/linux/sched.h
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+++ b/include/linux/sched.h
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@@ -1047,8 +1047,20 @@ struct wake_q_head {
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#define WAKE_Q(name) \
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struct wake_q_head name = { WAKE_Q_TAIL, &name.first }
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-extern void wake_q_add(struct wake_q_head *head,
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- struct task_struct *task);
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+extern void __wake_q_add(struct wake_q_head *head,
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+ struct task_struct *task, bool sleeper);
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+static inline void wake_q_add(struct wake_q_head *head,
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+ struct task_struct *task)
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+{
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+ __wake_q_add(head, task, false);
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+}
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+
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+static inline void wake_q_add_sleeper(struct wake_q_head *head,
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+ struct task_struct *task)
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+{
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+ __wake_q_add(head, task, true);
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+}
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+
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extern void __wake_up_q(struct wake_q_head *head, bool sleeper);
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static inline void wake_up_q(struct wake_q_head *head)
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@@ -1922,6 +1934,7 @@ struct task_struct {
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raw_spinlock_t pi_lock;
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struct wake_q_node wake_q;
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+ struct wake_q_node wake_q_sleeper;
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#ifdef CONFIG_RT_MUTEXES
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/* PI waiters blocked on a rt_mutex held by this task */
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diff --git a/kernel/fork.c b/kernel/fork.c
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index beb07138c728..e9cea5de947e 100644
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--- a/kernel/fork.c
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+++ b/kernel/fork.c
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@@ -572,6 +572,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
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tsk->splice_pipe = NULL;
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tsk->task_frag.page = NULL;
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tsk->wake_q.next = NULL;
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+ tsk->wake_q_sleeper.next = NULL;
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account_kernel_stack(tsk, 1);
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diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
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index 3fca4892ec51..f909d47c43d1 100644
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--- a/kernel/locking/rtmutex.c
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+++ b/kernel/locking/rtmutex.c
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@@ -1463,7 +1463,7 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
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*/
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preempt_disable();
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if (waiter->savestate)
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- wake_q_add(wake_sleeper_q, waiter->task);
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+ wake_q_add_sleeper(wake_sleeper_q, waiter->task);
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else
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wake_q_add(wake_q, waiter->task);
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raw_spin_unlock(¤t->pi_lock);
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diff --git a/kernel/sched/core.c b/kernel/sched/core.c
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index 303367c6cc2b..0f0d0cfe8161 100644
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -445,9 +445,15 @@ static bool set_nr_if_polling(struct task_struct *p)
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#endif
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#endif
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-void wake_q_add(struct wake_q_head *head, struct task_struct *task)
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+void __wake_q_add(struct wake_q_head *head, struct task_struct *task,
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+ bool sleeper)
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{
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- struct wake_q_node *node = &task->wake_q;
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+ struct wake_q_node *node;
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+
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+ if (sleeper)
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+ node = &task->wake_q_sleeper;
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+ else
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+ node = &task->wake_q;
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/*
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* Atomically grab the task, if ->wake_q is !nil already it means
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@@ -476,11 +482,17 @@ void __wake_up_q(struct wake_q_head *head, bool sleeper)
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while (node != WAKE_Q_TAIL) {
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struct task_struct *task;
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- task = container_of(node, struct task_struct, wake_q);
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+ if (sleeper)
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+ task = container_of(node, struct task_struct, wake_q_sleeper);
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+ else
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+ task = container_of(node, struct task_struct, wake_q);
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BUG_ON(!task);
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/* task can safely be re-inserted now */
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node = node->next;
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- task->wake_q.next = NULL;
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+ if (sleeper)
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+ task->wake_q_sleeper.next = NULL;
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+ else
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+ task->wake_q.next = NULL;
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/*
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* wake_up_process() implies a wmb() to pair with the queueing
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--
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2.28.0
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