[PATCH] powerpc: Fix deadlock in icswx code

Subsystems: linux for powerpc (32-bit and 64-bit), the rest

STALE5468d

3 messages, 2 authors, 2011-09-27 · open the first message on its own page

[PATCH] powerpc: Fix deadlock in icswx code

From: Anton Blanchard <hidden>
Date: 2011-09-14 19:43:15

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 <redacted>
Cc: <stable@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);

Re: [PATCH] powerpc: Fix deadlock in icswx code

From: Jimi Xenidis <hidden>
Date: 2011-09-15 13:09:52

On Sep 14, 2011, at 2:43 PM, Anton Blanchard wrote:


Hi Anton,
It would really help me a lot if you could review and maybe merge this =
with my earlier patch that splits this file.
  <http://patchwork.ozlabs.org/patch/109103/>
All it does is split.. I promise.
You don't have to take the other stuff.. yet :)

-JX

quoted hunk

=20
The icswx code introduced an A-B B-A deadlock:
=20
    CPU0                    CPU1
    ----                    ----
lock(&anon_vma->mutex);
                            lock(&mm->mmap_sem);
                            lock(&anon_vma->mutex);
lock(&mm->mmap_sem);
=20
Instead of using the mmap_sem to keep mm_users constant, take the
page table spinlock.
=20
Signed-off-by: Anton Blanchard <redacted>
Cc: <stable@kernel.org>
---
=20

diff --git a/arch/powerpc/mm/mmu_context_hash64.c =

b/arch/powerpc/mm/mmu_context_hash64.c

quoted hunk

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)

quoted hunk

	if (!mm || !acop)
		return -EINVAL;
=20
-	/* 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);
=20
	if (mm->context.cop_pid =3D=3D COP_PID_NONE) {

@@ -164,7 +164,7 @@ int use_cop(unsigned long acop, struct mm_struct =

*mm)

quoted hunk

=20
out:
	spin_unlock(mm->context.cop_lockp);
-	up_read(&mm->mmap_sem);
+	spin_unlock(&mm->page_table_lock);
=20
	return ret;
}

@@ -185,8 +185,8 @@ void drop_cop(unsigned long acop, struct mm_struct =

*mm)

quoted hunk

	if (WARN_ON_ONCE(!mm))
		return;
=20
-	/* 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);
=20
	mm->context.acop &=3D ~acop;

@@ -213,7 +213,7 @@ void drop_cop(unsigned long acop, struct mm_struct =

*mm)

	}
=20
	spin_unlock(mm->context.cop_lockp);
-	up_read(&mm->mmap_sem);
+	spin_unlock(&mm->page_table_lock);
}
EXPORT_SYMBOL_GPL(drop_cop);
=20
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Re: [PATCH] powerpc: Fix deadlock in icswx code

From: Anton Blanchard <hidden>
Date: 2011-09-27 10:04:59

Hi Jimi,

It would really help me a lot if you could review and maybe merge
this with my earlier patch that splits this file.
<http://patchwork.ozlabs.org/patch/109103/> All it does is split.. I
promise. You don't have to take the other stuff.. yet :)

Sorry it took so long to get to this. Looking at it now.

Anton

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