[PATCH] powerpc: Fix deadlock in icswx code

[Anton Blanchard]

The icswx code introduced an A-B B-A deadlock:

     CPU0                    CPU1
     ----                    ----
lock(&anon_vma->mutex);
                             lock(&mm->mmap_sem);
                             lock(&anon_vma->mutex);
lock(&mm->mmap_sem);

Instead of using the mmap_sem to keep mm_users constant, take the
page table spinlock.

Signed-off-by: Anton Blanchard <an...@samba.org>
Cc: <sta...@kernel.org>
---

diff --git a/arch/powerpc/mm/mmu_context_hash64.c 
b/arch/powerpc/mm/mmu_context_hash64.c
index 3bafc3d..4ff587e 100644
--- a/arch/powerpc/mm/mmu_context_hash64.c
+++ b/arch/powerpc/mm/mmu_context_hash64.c
@@ -136,8 +136,8 @@ int use_cop(unsigned long acop, struct mm_struct *mm)
        if (!mm || !acop)
                return -EINVAL;
 
-       /* We need to make sure mm_users doesn't change */
-       down_read(&mm->mmap_sem);
+       /* The page_table_lock ensures mm_users won't change under us */
+       spin_lock(&mm->page_table_lock);
        spin_lock(mm->context.cop_lockp);
 
        if (mm->context.cop_pid == COP_PID_NONE) {
@@ -164,7 +164,7 @@ int use_cop(unsigned long acop, struct mm_struct *mm)
 
 out:
        spin_unlock(mm->context.cop_lockp);
-       up_read(&mm->mmap_sem);
+       spin_unlock(&mm->page_table_lock);
 
        return ret;
 }
@@ -185,8 +185,8 @@ void drop_cop(unsigned long acop, struct mm_struct *mm)
        if (WARN_ON_ONCE(!mm))
                return;
 
-       /* We need to make sure mm_users doesn't change */
-       down_read(&mm->mmap_sem);
+       /* The page_table_lock ensures mm_users won't change under us */
+       spin_lock(&mm->page_table_lock);
        spin_lock(mm->context.cop_lockp);
 
        mm->context.acop &= ~acop;
@@ -213,7 +213,7 @@ void drop_cop(unsigned long acop, struct mm_struct *mm)
        }
 
        spin_unlock(mm->context.cop_lockp);
-       up_read(&mm->mmap_sem);
+       spin_unlock(&mm->page_table_lock);
 }
 EXPORT_SYMBOL_GPL(drop_cop);
 
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