190 lines
6.0 KiB
Diff
190 lines
6.0 KiB
Diff
From ce774d63bdfdcbcb5b8e1b3fb303fc1db4866313 Mon Sep 17 00:00:00 2001
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From: Xunlei Pang <xlpang@redhat.com>
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Date: Thu, 23 Mar 2017 15:56:07 +0100
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Subject: [PATCH 018/365] rtmutex: Deboost before waking up the top waiter
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Upstream commit 2a1c6029940675abb2217b590512dbf691867ec4
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We should deboost before waking the high-priority task, such that we
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don't run two tasks with the same "state" (priority, deadline,
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sched_class, etc).
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In order to make sure the boosting task doesn't start running between
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unlock and deboost (due to 'spurious' wakeup), we move the deboost
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under the wait_lock, that way its serialized against the wait loop in
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__rt_mutex_slowlock().
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Doing the deboost early can however lead to priority-inversion if
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current would get preempted after the deboost but before waking our
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high-prio task, hence we disable preemption before doing deboost, and
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enabling it after the wake up is over.
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This gets us the right semantic order, but most importantly however;
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this change ensures pointer stability for the next patch, where we
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have rt_mutex_setprio() cache a pointer to the top-most waiter task.
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If we, as before this change, do the wakeup first and then deboost,
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this pointer might point into thin air.
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[peterz: Changelog + patch munging]
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Suggested-by: Peter Zijlstra <peterz@infradead.org>
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Signed-off-by: Xunlei Pang <xlpang@redhat.com>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Acked-by: Steven Rostedt <rostedt@goodmis.org>
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Cc: juri.lelli@arm.com
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Cc: bigeasy@linutronix.de
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Cc: mathieu.desnoyers@efficios.com
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Cc: jdesfossez@efficios.com
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Cc: bristot@redhat.com
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Link: http://lkml.kernel.org/r/20170323150216.110065320@infradead.org
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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kernel/futex.c | 5 +--
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kernel/locking/rtmutex.c | 59 ++++++++++++++++++---------------
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kernel/locking/rtmutex_common.h | 2 +-
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3 files changed, 34 insertions(+), 32 deletions(-)
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diff --git a/kernel/futex.c b/kernel/futex.c
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index 4dfa778e7cb1..f8a35ec29c28 100644
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -1476,10 +1476,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_
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out_unlock:
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raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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- if (deboost) {
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- wake_up_q(&wake_q);
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- rt_mutex_adjust_prio(current);
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- }
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+ rt_mutex_postunlock(&wake_q, deboost);
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return ret;
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}
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diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
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index 7f8ee5d61ce9..a77f7cae7ca0 100644
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--- a/kernel/locking/rtmutex.c
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+++ b/kernel/locking/rtmutex.c
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@@ -369,24 +369,6 @@ static void __rt_mutex_adjust_prio(struct task_struct *task)
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rt_mutex_setprio(task, prio);
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}
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-/*
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- * Adjust task priority (undo boosting). Called from the exit path of
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- * rt_mutex_slowunlock() and rt_mutex_slowlock().
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- *
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- * (Note: We do this outside of the protection of lock->wait_lock to
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- * allow the lock to be taken while or before we readjust the priority
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- * of task. We do not use the spin_xx_mutex() variants here as we are
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- * outside of the debug path.)
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- */
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-void rt_mutex_adjust_prio(struct task_struct *task)
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-{
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- unsigned long flags;
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-
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- raw_spin_lock_irqsave(&task->pi_lock, flags);
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- __rt_mutex_adjust_prio(task);
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- raw_spin_unlock_irqrestore(&task->pi_lock, flags);
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-}
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-
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/*
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* Deadlock detection is conditional:
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*
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@@ -1072,6 +1054,7 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
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* lock->wait_lock.
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*/
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rt_mutex_dequeue_pi(current, waiter);
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+ __rt_mutex_adjust_prio(current);
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/*
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* As we are waking up the top waiter, and the waiter stays
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@@ -1416,6 +1399,16 @@ static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
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*/
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mark_wakeup_next_waiter(wake_q, lock);
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+ /*
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+ * We should deboost before waking the top waiter task such that
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+ * we don't run two tasks with the 'same' priority. This however
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+ * can lead to prio-inversion if we would get preempted after
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+ * the deboost but before waking our high-prio task, hence the
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+ * preempt_disable before unlock. Pairs with preempt_enable() in
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+ * rt_mutex_postunlock();
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+ */
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+ preempt_disable();
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+
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raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
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/* check PI boosting */
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@@ -1465,6 +1458,18 @@ rt_mutex_fasttrylock(struct rt_mutex *lock,
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return slowfn(lock);
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}
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+/*
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+ * Undo pi boosting (if necessary) and wake top waiter.
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+ */
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+void rt_mutex_postunlock(struct wake_q_head *wake_q, bool deboost)
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+{
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+ wake_up_q(wake_q);
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+
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+ /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
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+ if (deboost)
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+ preempt_enable();
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+}
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+
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static inline void
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rt_mutex_fastunlock(struct rt_mutex *lock,
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bool (*slowfn)(struct rt_mutex *lock,
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@@ -1478,11 +1483,7 @@ rt_mutex_fastunlock(struct rt_mutex *lock,
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deboost = slowfn(lock, &wake_q);
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- wake_up_q(&wake_q);
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-
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- /* Undo pi boosting if necessary: */
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- if (deboost)
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- rt_mutex_adjust_prio(current);
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+ rt_mutex_postunlock(&wake_q, deboost);
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}
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/**
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@@ -1595,6 +1596,13 @@ bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
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}
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mark_wakeup_next_waiter(wake_q, lock);
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+ /*
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+ * We've already deboosted, retain preempt_disabled when dropping
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+ * the wait_lock to avoid inversion until the wakeup. Matched
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+ * by rt_mutex_postunlock();
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+ */
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+ preempt_disable();
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+
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return true; /* deboost and wakeups */
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}
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@@ -1607,10 +1615,7 @@ void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
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deboost = __rt_mutex_futex_unlock(lock, &wake_q);
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raw_spin_unlock_irq(&lock->wait_lock);
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- if (deboost) {
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- wake_up_q(&wake_q);
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- rt_mutex_adjust_prio(current);
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- }
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+ rt_mutex_postunlock(&wake_q, deboost);
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}
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/**
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diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
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index f4c34c4195a0..dad9229040dc 100644
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--- a/kernel/locking/rtmutex_common.h
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+++ b/kernel/locking/rtmutex_common.h
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@@ -123,7 +123,7 @@ extern void rt_mutex_futex_unlock(struct rt_mutex *lock);
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extern bool __rt_mutex_futex_unlock(struct rt_mutex *lock,
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struct wake_q_head *wqh);
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-extern void rt_mutex_adjust_prio(struct task_struct *task);
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+extern void rt_mutex_postunlock(struct wake_q_head *wake_q, bool deboost);
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#ifdef CONFIG_DEBUG_RT_MUTEXES
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# include "rtmutex-debug.h"
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--
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2.28.0
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