[SPARC64]: Bulletproof MMU context locking.

1) Always spin_lock_init() in init_context().  The caller essentially
   clears it out, or copies the mm info from the parent.  In both
   cases we need to explicitly initialize the spinlock.

2) Always do explicit IRQ disabling while taking mm->context.lock
   and ctx_alloc_lock.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc64/mm/init.c

@@ -639,9 +639,10 @@ void get_new_mmu_context(struct mm_struct *mm)
 {
 	unsigned long ctx, new_ctx;
 	unsigned long orig_pgsz_bits;
+	unsigned long flags;
 	int new_version;
 
-	spin_lock(&ctx_alloc_lock);
+	spin_lock_irqsave(&ctx_alloc_lock, flags);
 	orig_pgsz_bits = (mm->context.sparc64_ctx_val & CTX_PGSZ_MASK);
 	ctx = (tlb_context_cache + 1) & CTX_NR_MASK;
 	new_ctx = find_next_zero_bit(mmu_context_bmap, 1 << CTX_NR_BITS, ctx);
@@ -677,7 +678,7 @@ void get_new_mmu_context(struct mm_struct *mm)
 out:
 	tlb_context_cache = new_ctx;
 	mm->context.sparc64_ctx_val = new_ctx | orig_pgsz_bits;
-	spin_unlock(&ctx_alloc_lock);
+	spin_unlock_irqrestore(&ctx_alloc_lock, flags);
 
 	if (unlikely(new_version))
 		smp_new_mmu_context_version();

arch/sparc64/mm/tsb.c

@@ -354,6 +354,7 @@ void tsb_grow(struct mm_struct *mm, unsigned long rss, gfp_t gfp_flags)
 
 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 {
+	spin_lock_init(&mm->context.lock);
 
 	mm->context.sparc64_ctx_val = 0UL;
 

include/asm-sparc64/mmu_context.h

@@ -67,14 +67,14 @@ extern void __flush_tlb_mm(unsigned long, unsigned long);
 /* Switch the current MM context.  Interrupts are disabled.  */
 static inline void switch_mm(struct mm_struct *old_mm, struct mm_struct *mm, struct task_struct *tsk)
 {
-	unsigned long ctx_valid;
+	unsigned long ctx_valid, flags;
 	int cpu;
 
-	spin_lock(&mm->context.lock);
+	spin_lock_irqsave(&mm->context.lock, flags);
 	ctx_valid = CTX_VALID(mm->context);
 	if (!ctx_valid)
 		get_new_mmu_context(mm);
-	spin_unlock(&mm->context.lock);
+	spin_unlock_irqrestore(&mm->context.lock, flags);
 
 	if (!ctx_valid || (old_mm != mm)) {
 		load_secondary_context(mm);