From b46b6942b39e577fe3ef1af928cd927864011247 Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Tue, 2 Jun 2009 18:53:37 +0000 Subject: [PATCH] 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 --- arch/powerpc/mm/mmu_context_nohash.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/mm/mmu_context_nohash.c b/arch/powerpc/mm/mmu_context_nohash.c index c428587..8343986 100644 --- a/arch/powerpc/mm/mmu_context_nohash.c +++ b/arch/powerpc/mm/mmu_context_nohash.c @@ -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 -- 1.8.2.3