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powerpc/mm: Fix a AB->BA deadlock scenario with nohash MMU context lock
The MMU context_lock can be taken from switch_mm() while the rq->lock is held. The rq->lock can also be taken from interrupts, thus if we get interrupted in destroy_context() with the context lock held and that interrupt tries to take the rq->lock, there's a possible deadlock scenario with another CPU having the rq->lock and calling switch_mm() which takes our context lock. The fix is to always ensure interrupts are off when taking our context lock. The switch_mm() path is already good so this fixes the destroy_context() path. While at it, turn the context lock into a new style spinlock. Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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@ -46,7 +46,7 @@ static unsigned int next_context, nr_free_contexts;
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static unsigned long *context_map;
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static unsigned long *stale_map[NR_CPUS];
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static struct mm_struct **context_mm;
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static spinlock_t context_lock = SPIN_LOCK_UNLOCKED;
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static DEFINE_SPINLOCK(context_lock);
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#define CTX_MAP_SIZE \
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(sizeof(unsigned long) * (last_context / BITS_PER_LONG + 1))
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@ -276,6 +276,7 @@ int init_new_context(struct task_struct *t, struct mm_struct *mm)
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*/
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void destroy_context(struct mm_struct *mm)
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{
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unsigned long flags;
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unsigned int id;
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if (mm->context.id == MMU_NO_CONTEXT)
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@ -283,7 +284,7 @@ void destroy_context(struct mm_struct *mm)
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WARN_ON(mm->context.active != 0);
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spin_lock(&context_lock);
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spin_lock_irqsave(&context_lock, flags);
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id = mm->context.id;
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if (id != MMU_NO_CONTEXT) {
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__clear_bit(id, context_map);
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@ -294,7 +295,7 @@ void destroy_context(struct mm_struct *mm)
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context_mm[id] = NULL;
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nr_free_contexts++;
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}
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spin_unlock(&context_lock);
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spin_unlock_irqrestore(&context_lock, flags);
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}
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#ifdef CONFIG_SMP
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