[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[Thomas Gleixner]

When lockdep traces a lock taken in a module the arm unwinder takes
unwind_lock which causes a recursive lockdep call deadlocking itself
on the unwind_lock.

Make unwind_lock an arch_spin_lock to avoid the lockdep call and use
the raw_local_irq_save/restore() variants to avoid irq tracing as
well.

Reported-and-tested-by: Torben Hohn <torbenh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable at kernel.org
---
 arch/arm/kernel/unwind.c |   20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

Index: linux-2.6/arch/arm/kernel/unwind.c
===================================================================
--- linux-2.6.orig/arch/arm/kernel/unwind.c
+++ linux-2.6/arch/arm/kernel/unwind.c
@@ -86,7 +86,7 @@ enum regs {
 extern struct unwind_idx __start_unwind_idx[];
 extern struct unwind_idx __stop_unwind_idx[];
 
-static DEFINE_SPINLOCK(unwind_lock);
+static arch_spinlock_t unwind_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
 static LIST_HEAD(unwind_tables);
 
 /* Convert a prel31 symbol to an absolute address */
@@ -140,7 +140,8 @@ static struct unwind_idx *unwind_find_id
 		/* module unwind tables */
 		struct unwind_table *table;
 
-		spin_lock_irqsave(&unwind_lock, flags);
+		raw_local_irq_save(flags);
+		arch_spin_lock(&unwind_lock);
 		list_for_each_entry(table, &unwind_tables, list) {
 			if (addr >= table->begin_addr &&
 			    addr < table->end_addr) {
@@ -151,7 +152,8 @@ static struct unwind_idx *unwind_find_id
 				break;
 			}
 		}
-		spin_unlock_irqrestore(&unwind_lock, flags);
+		arch_spin_unlock(&unwind_lock);
+		raw_local_irq_restore(flags);
 	}
 
 	pr_debug("%s: idx = %p\n", __func__, idx);
@@ -417,9 +419,11 @@ struct unwind_table *unwind_table_add(un
 	for (idx = tab->start; idx < tab->stop; idx++)
 		idx->addr = prel31_to_addr(&idx->addr);
 
-	spin_lock_irqsave(&unwind_lock, flags);
+	raw_local_irq_save(flags);
+	arch_spin_lock(&unwind_lock);
 	list_add_tail(&tab->list, &unwind_tables);
-	spin_unlock_irqrestore(&unwind_lock, flags);
+	arch_spin_unlock(&unwind_lock);
+	raw_local_irq_restore(flags);
 
 	return tab;
 }
@@ -431,9 +435,11 @@ void unwind_table_del(struct unwind_tabl
 	if (!tab)
 		return;
 
-	spin_lock_irqsave(&unwind_lock, flags);
+	raw_local_irq_save(flags);
+	arch_spin_lock(&unwind_lock);
 	list_del(&tab->list);
-	spin_unlock_irqrestore(&unwind_lock, flags);
+	arch_spin_unlock(&unwind_lock);
+	raw_local_irq_restore(flags);
 
 	kfree(tab);
 }

[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[Peter Zijlstra]

On Tue, 2011-05-17 at 16:11 +0200, Thomas Gleixner wrote:
> When lockdep traces a lock taken in a module the arm unwinder takes
> unwind_lock which causes a recursive lockdep call deadlocking itself
> on the unwind_lock.
> 
> Make unwind_lock an arch_spin_lock to avoid the lockdep call and use
> the raw_local_irq_save/restore() variants to avoid irq tracing as
> well. 

That doesn't parse, lockdep has recursion protection, this shouldn't
happen.

[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[Catalin Marinas]

On 17 May 2011 15:11, Thomas Gleixner <tglx@linutronix.de> wrote:
> When lockdep traces a lock taken in a module the arm unwinder takes
> unwind_lock which causes a recursive lockdep call deadlocking itself
> on the unwind_lock.
>
> Make unwind_lock an arch_spin_lock to avoid the lockdep call and use
> the raw_local_irq_save/restore() variants to avoid irq tracing as
> well.
>
> Reported-and-tested-by: Torben Hohn <torbenh@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: stable at kernel.org

Looks fine to me (as the author of this code):

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[Thomas Gleixner]

On Tue, 17 May 2011, Peter Zijlstra wrote:

> On Tue, 2011-05-17 at 16:11 +0200, Thomas Gleixner wrote:
> > When lockdep traces a lock taken in a module the arm unwinder takes
> > unwind_lock which causes a recursive lockdep call deadlocking itself
> > on the unwind_lock.
> > 
> > Make unwind_lock an arch_spin_lock to avoid the lockdep call and use
> > the raw_local_irq_save/restore() variants to avoid irq tracing as
> > well. 
> 
> That doesn't parse, lockdep has recursion protection, this shouldn't
> happen.

Gah, misread the splat. The problem is 

     unwind() -> lock() -> lock_acquired() -> unwind() -> lock()

So it's not lockdep calling first. Will resend with a proper
changelog.

Thanks,

	tglx

[PATCH] arm: Use arch_spin_lock for unwind to avoid lockdep deadlock

[Thomas Gleixner]

On Tue, 17 May 2011, Thomas Gleixner wrote:

> On Tue, 17 May 2011, Peter Zijlstra wrote:
> 
> > On Tue, 2011-05-17 at 16:11 +0200, Thomas Gleixner wrote:
> > > When lockdep traces a lock taken in a module the arm unwinder takes
> > > unwind_lock which causes a recursive lockdep call deadlocking itself
> > > on the unwind_lock.
> > > 
> > > Make unwind_lock an arch_spin_lock to avoid the lockdep call and use
> > > the raw_local_irq_save/restore() variants to avoid irq tracing as
> > > well. 
> > 
> > That doesn't parse, lockdep has recursion protection, this shouldn't
> > happen.
> 
> Gah, misread the splat. The problem is 
> 
>      unwind() -> lock() -> lock_acquired() -> unwind() -> lock()

Grmpf, no. That does not make sense as the stack trace is taken in
lock_aquire() which happens before lock(). Ignore that for now until I
have it reproduced.

Thanks,

	tglx