44 lines
1.5 KiB
Diff
44 lines
1.5 KiB
Diff
From: Thomas Gleixner <tglx@linutronix.de>
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Date: Fri, 1 Mar 2013 11:17:42 +0100
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Subject: futex: Ensure lock/unlock symetry versus pi_lock and hash bucket lock
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz
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In exit_pi_state_list() we have the following locking construct:
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spin_lock(&hb->lock);
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raw_spin_lock_irq(&curr->pi_lock);
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...
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spin_unlock(&hb->lock);
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In !RT this works, but on RT the migrate_enable() function which is
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called from spin_unlock() sees atomic context due to the held pi_lock
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and just decrements the migrate_disable_atomic counter of the
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task. Now the next call to migrate_disable() sees the counter being
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negative and issues a warning. That check should be in
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migrate_enable() already.
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Fix this by dropping pi_lock before unlocking hb->lock and reaquire
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pi_lock after that again. This is safe as the loop code reevaluates
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head again under the pi_lock.
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Reported-by: Yong Zhang <yong.zhang@windriver.com>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/futex.c | 2 ++
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1 file changed, 2 insertions(+)
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -918,7 +918,9 @@ void exit_pi_state_list(struct task_stru
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if (head->next != next) {
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/* retain curr->pi_lock for the loop invariant */
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raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
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+ raw_spin_unlock_irq(&curr->pi_lock);
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spin_unlock(&hb->lock);
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+ raw_spin_lock_irq(&curr->pi_lock);
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put_pi_state(pi_state);
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continue;
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}
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