[PATCH RT] arm/unwind: fail on unwind in irq disabled regions

[PATCH RT] arm/unwind: fail on unwind in irq disabled regions

[Sebastian Andrzej Siewior]

Mostly unwind is done with irqs enabled however SLUB may call it with
irqs disabled while creating a new SLUB cache.

I had system freeze while loading a module which called
kmem_cache_create() on init. That means SLUB's __slab_alloc() disabled
interrupts and then

->new_slab_objects()
 ->new_slab()
  ->setup_object()
   ->setup_object_debug()
    ->init_tracking()
     ->set_track()
      ->save_stack_trace()
       ->save_stack_trace_tsk()
        ->walk_stackframe()
         ->unwind_frame()
          ->unwind_find_idx()
           =>spin_lock_irqsave(&unwind_lock);

I would prefer not to turn this into a raw lock so for now it will just
fail if it is called with irqs disabled which might return a few "empty"
traces…

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/arm/kernel/unwind.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index 00df012..2af232d 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -195,6 +195,11 @@ static const struct unwind_idx *unwind_find_idx(unsigned long addr)
 		/* module unwind tables */
 		struct unwind_table *table;
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+		if (irqs_disabled())
+			goto out;
+#endif
+
 		spin_lock_irqsave(&unwind_lock, flags);
 		list_for_each_entry(table, &unwind_tables, list) {
 			if (addr >= table->begin_addr &&
@@ -211,6 +216,7 @@ static const struct unwind_idx *unwind_find_idx(unsigned long addr)
 	}
 
 	pr_debug("%s: idx = %p\n", __func__, idx);
+out:
 	return idx;
 }
 
@@ -345,7 +351,9 @@ int unwind_frame(struct stackframe *frame)
 
 	idx = unwind_find_idx(frame->pc);
 	if (!idx) {
+#ifndef CONFIG_PREEMPT_RT_FULL
 		pr_warning("unwind: Index not found %08lx\n", frame->pc);
+#endif
 		return -URC_FAILURE;
 	}
 
-- 
1.8.5.3

Re: [PATCH RT] arm/unwind: fail on unwind in irq disabled regions

[Thomas Gleixner]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 988 bytes --]



On Fri, 24 Jan 2014, Sebastian Andrzej Siewior wrote:

> Mostly unwind is done with irqs enabled however SLUB may call it with
> irqs disabled while creating a new SLUB cache.
> 
> I had system freeze while loading a module which called
> kmem_cache_create() on init. That means SLUB's __slab_alloc() disabled
> interrupts and then
> 
> ->new_slab_objects()
>  ->new_slab()
>   ->setup_object()
>    ->setup_object_debug()
>     ->init_tracking()
>      ->set_track()
>       ->save_stack_trace()
>        ->save_stack_trace_tsk()
>         ->walk_stackframe()
>          ->unwind_frame()
>           ->unwind_find_idx()
>            =>spin_lock_irqsave(&unwind_lock);
> 
> I would prefer not to turn this into a raw lock so for now it will just
> fail if it is called with irqs disabled which might return a few "empty"
> traces…

If we really end up with unwinding then the few cycles to follow the
stack are not that important anymore. We really want that output.

Thanks,

	tglx

Re: [PATCH RT] arm/unwind: fail on unwind in irq disabled regions

[Sebastian Andrzej Siewior]

* Thomas Gleixner | 2014-02-13 23:57:45 [+0100]:

>If we really end up with unwinding then the few cycles to follow the
>stack are not that important anymore. We really want that output.

Here you go.

diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index 2af232d..bbafc67 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -87,7 +87,7 @@ extern const struct unwind_idx __start_unwind_idx[];
 static const struct unwind_idx *__origin_unwind_idx;
 extern const struct unwind_idx __stop_unwind_idx[];
 
-static DEFINE_SPINLOCK(unwind_lock);
+static DEFINE_RAW_SPINLOCK(unwind_lock);
 static LIST_HEAD(unwind_tables);
 
 /* Convert a prel31 symbol to an absolute address */
@@ -195,12 +195,7 @@ static const struct unwind_idx *unwind_find_idx(unsigned long addr)
 		/* module unwind tables */
 		struct unwind_table *table;
 
-#ifdef CONFIG_PREEMPT_RT_FULL
-		if (irqs_disabled())
-			goto out;
-#endif
-
-		spin_lock_irqsave(&unwind_lock, flags);
+		raw_spin_lock_irqsave(&unwind_lock, flags);
 		list_for_each_entry(table, &unwind_tables, list) {
 			if (addr >= table->begin_addr &&
 			    addr < table->end_addr) {
@@ -212,11 +207,10 @@ static const struct unwind_idx *unwind_find_idx(unsigned long addr)
 				break;
 			}
 		}
-		spin_unlock_irqrestore(&unwind_lock, flags);
+		raw_spin_unlock_irqrestore(&unwind_lock, flags);
 	}
 
 	pr_debug("%s: idx = %p\n", __func__, idx);
-out:
 	return idx;
 }
 
@@ -351,9 +345,7 @@ int unwind_frame(struct stackframe *frame)
 
 	idx = unwind_find_idx(frame->pc);
 	if (!idx) {
-#ifndef CONFIG_PREEMPT_RT_FULL
 		pr_warning("unwind: Index not found %08lx\n", frame->pc);
-#endif
 		return -URC_FAILURE;
 	}
 
@@ -477,9 +469,9 @@ struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
 	tab->begin_addr = text_addr;
 	tab->end_addr = text_addr + text_size;
 
-	spin_lock_irqsave(&unwind_lock, flags);
+	raw_spin_lock_irqsave(&unwind_lock, flags);
 	list_add_tail(&tab->list, &unwind_tables);
-	spin_unlock_irqrestore(&unwind_lock, flags);
+	raw_spin_unlock_irqrestore(&unwind_lock, flags);
 
 	return tab;
 }
@@ -491,9 +483,9 @@ void unwind_table_del(struct unwind_table *tab)
 	if (!tab)
 		return;
 
-	spin_lock_irqsave(&unwind_lock, flags);
+	raw_spin_lock_irqsave(&unwind_lock, flags);
 	list_del(&tab->list);
-	spin_unlock_irqrestore(&unwind_lock, flags);
+	raw_spin_unlock_irqrestore(&unwind_lock, flags);
 
 	kfree(tab);
 }
-- 
1.9.0.rc3

>Thanks,
>
>	tglx

Sebastian