[3.16.y-ckt stable] Patch "sparc32: destroy_context() and switch_mm() needs to disable interrupts." has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    sparc32: destroy_context() and switch_mm() needs to disable interrupts.

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 99fd9e231ce7af5863670aa82963aa37d2b1af3a Mon Sep 17 00:00:00 2001
From: Andreas Larsson <andreas at gaisler.com>
Date: Thu, 18 Dec 2014 13:23:23 +0100
Subject: sparc32: destroy_context() and switch_mm() needs to disable
 interrupts.

commit 66d0f7ec9f1038452178b1993fc07fd96d30fd38 upstream.

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 <andreas at gaisler.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 be65f035d18a..5cbc96d801ff 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;
 	}
 }