Subject: [PATCH 1/6] sparc32: destroy_context() and switch_mm() needs to disable interrupts.

From: Andreas Larsson <[email-masked]>
Date: Thu, 18 Dec 2014 13:23:23 +0100

[ Upstream commit 66d0f7ec9f1038452178b1993fc07fd96d30fd38 ]

Load balancing can be triggered in the critical sections protected by
srmmu_context_spinlock in destroy_context() and switch_mm() and can hang
the cpu waiting for the rq lock of another cpu that in turn has called
switch_mm hangning on srmmu_context_spinlock leading to deadlock.

So, disable interrupt while taking srmmu_context_spinlock in
destroy_context() and switch_mm() so we don't deadlock.

See also commit 77b838fa1ef0 ("[SPARC64]: destroy_context() needs to disable
interrupts.")

Signed-off-by: Andreas Larsson <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 arch/sparc/mm/srmmu.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/sparc/mm/srmmu.c b/arch/sparc/mm/srmmu.c
index be65f03..5cbc96d 100644
--- a/arch/sparc/mm/srmmu.c
+++ b/arch/sparc/mm/srmmu.c
@@ -460,10 +460,12 @@ static void __init sparc_context_init(int numctx)
 void switch_mm(struct mm_struct *old_mm, struct mm_struct *mm,
 	       struct task_struct *tsk)
 {
+	unsigned long flags;
+
 	if (mm->context == NO_CONTEXT) {
-		spin_lock(&srmmu_context_spinlock);
+		spin_lock_irqsave(&srmmu_context_spinlock, flags);
 		alloc_context(old_mm, mm);
-		spin_unlock(&srmmu_context_spinlock);
+		spin_unlock_irqrestore(&srmmu_context_spinlock, flags);
 		srmmu_ctxd_set(&srmmu_context_table[mm->context], mm->pgd);
 	}
 
@@ -986,14 +988,15 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 
 void destroy_context(struct mm_struct *mm)
 {
+	unsigned long flags;
 
 	if (mm->context != NO_CONTEXT) {
 		flush_cache_mm(mm);
 		srmmu_ctxd_set(&srmmu_context_table[mm->context], srmmu_swapper_pg_dir);
 		flush_tlb_mm(mm);
-		spin_lock(&srmmu_context_spinlock);
+		spin_lock_irqsave(&srmmu_context_spinlock, flags);
 		free_context(mm->context);
-		spin_unlock(&srmmu_context_spinlock);
+		spin_unlock_irqrestore(&srmmu_context_spinlock, flags);
 		mm->context = NO_CONTEXT;
 	}
 }
-- 
1.7.11.7