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67 lines
2.4 KiB
Diff
67 lines
2.4 KiB
Diff
From: Thomas Gleixner <tglx@linutronix.de>
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Date: Wed, 8 Mar 2017 14:23:35 +0100
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Subject: [PATCH] futex: workaround migrate_disable/enable in different context
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migrate_enable() invokes __schedule() and it expects a preempt count of one.
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Holding a raw_spinlock_t with disabled interrupts should not allow scheduling.
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These little hacks ensure that we don't schedule while we lock the hb lockwith
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interrupts enabled and unlock it with interrupts disabled.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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[XXX: As per PeterZ suggesstion
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set_thread_flag(TIF_NEED_RESCHED); preempt_fold_need_resched()
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would trigger a scheduler invocation on the last preempt_enable() which in
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turn would allow to drop this.
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]
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/futex.c | 18 ++++++++++++++++++
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1 file changed, 18 insertions(+)
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -2997,6 +2997,14 @@ static int futex_lock_pi(u32 __user *uad
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* before __rt_mutex_start_proxy_lock() is done.
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*/
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raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
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+ /*
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+ * the migrate_disable() here disables migration in the in_atomic() fast
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+ * path which is enabled again in the following spin_unlock(). We have
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+ * one migrate_disable() pending in the slow-path which is reversed
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+ * after the raw_spin_unlock_irq() where we leave the atomic context.
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+ */
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+ migrate_disable();
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+
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spin_unlock(q.lock_ptr);
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/*
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* __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
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@@ -3005,6 +3013,7 @@ static int futex_lock_pi(u32 __user *uad
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*/
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ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
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raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
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+ migrate_enable();
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if (ret) {
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if (ret == 1)
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@@ -3153,10 +3162,19 @@ static int futex_unlock_pi(u32 __user *u
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* rt_waiter. Also see the WARN in wake_futex_pi().
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*/
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raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
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+ /*
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+ * Magic trickery for now to make the RT migrate disable
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+ * logic happy. The following spin_unlock() happens with
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+ * interrupts disabled so the internal migrate_enable()
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+ * won't undo the migrate_disable() which was issued when
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+ * locking hb->lock.
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+ */
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+ migrate_disable();
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spin_unlock(&hb->lock);
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/* drops pi_state->pi_mutex.wait_lock */
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ret = wake_futex_pi(uaddr, uval, pi_state);
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+ migrate_enable();
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put_pi_state(pi_state);
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