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Commit b46b6942 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt
Browse files

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: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 3035c863

arch/powerpc/mm/mmu_context_nohash.c

+4 −3
Original line number Diff line number Diff line
@@ -46,7 +46,7 @@ static unsigned int next_context, nr_free_contexts; 
static unsigned long *context_map;

static unsigned long *stale_map[NR_CPUS];

static struct mm_struct **context_mm;

static spinlock_t context_lock = SPIN_LOCK_UNLOCKED;

static DEFINE_SPINLOCK(context_lock);



#define CTX_MAP_SIZE	\

	(sizeof(unsigned long) * (last_context / BITS_PER_LONG + 1))
@@ -276,6 +276,7 @@ int init_new_context(struct task_struct *t, struct mm_struct *mm) 
 */

void destroy_context(struct mm_struct *mm)

{

	unsigned long flags;

	unsigned int id;



	if (mm->context.id == MMU_NO_CONTEXT)
@@ -283,7 +284,7 @@ void destroy_context(struct mm_struct *mm) 


	WARN_ON(mm->context.active != 0);



	spin_lock(&context_lock);

	spin_lock_irqsave(&context_lock, flags);

	id = mm->context.id;

	if (id != MMU_NO_CONTEXT) {

		__clear_bit(id, context_map);
@@ -294,7 +295,7 @@ void destroy_context(struct mm_struct *mm) 
		context_mm[id] = NULL;

		nr_free_contexts++;

	}

	spin_unlock(&context_lock);

	spin_unlock_irqrestore(&context_lock, flags);

}



#ifdef CONFIG_SMP