linux-kernel - Re: [PATCH] Ftrace: irqsoff tracer may cause stack overflow

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Date:	Fri, 8 Jan 2010 06:18:48 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Li Yi <yi.li@...log.com>
Cc:	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [PATCH] Ftrace: irqsoff tracer may cause stack overflow

On Fri, Jan 08, 2010 at 12:45:25PM +0800, Li Yi wrote:
> "irqsoff" tracer may cause stack overflow on architectures using
> asm-generic/atomic.h, due to recursive invoking of, e.g.
> trace_hardirqs_off().
> 
> trace_hardirqs_off() -> start_critical_timing() -> atomic_inc() ->
> atomic_add_return() -> local_irq_save() -> trace_hardirqs_off()
> 
> Signed-off-by: Yi Li <yi.li@...log.com>



Good catch!

However, may be we should keep the local_irq_save there
and have __raw_atomic_* versions only for tracing.

It's better to keep track of most irq disabled sites.

Why not something like the following (untested):


diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h
index c99c64d..ffc6772 100644
--- a/include/asm-generic/atomic.h
+++ b/include/asm-generic/atomic.h
@@ -17,6 +17,14 @@
 #error not SMP safe
 #endif
 
+#ifdef __ATOMIC_NEED_RAW_IRQ_SAVE
+#define __atomic_op_irq_save(f)		raw_local_irq_save(f)
+#define __atomic_op_irq_restore(f)	raw_local_irq_restore(f)
+#else
+#define __atomic_op_irq_save(f)		local_irq_save(f)
+#define __atomic_op_irq_restore(f)	local_irq_restore(f)
+#endif
+
 /*
  * Atomic operations that C can't guarantee us.  Useful for
  * resource counting etc..
@@ -60,11 +68,11 @@ static inline int atomic_add_return(int i, atomic_t *v)
 	unsigned long flags;
 	int temp;
 
-	local_irq_save(flags);
+	__atomic_op_irq_save(flags);
 	temp = v->counter;
 	temp += i;
 	v->counter = temp;
-	local_irq_restore(flags);
+	__atomic_op_irq_restore(flags);
 
 	return temp;
 }
@@ -82,11 +90,11 @@ static inline int atomic_sub_return(int i, atomic_t *v)
 	unsigned long flags;
 	int temp;
 
-	local_irq_save(flags);
+	__atomic_op_irq_save(flags);
 	temp = v->counter;
 	temp -= i;
 	v->counter = temp;
-	local_irq_restore(flags);
+	__atomic_op_irq_restore(flags);
 
 	return temp;
 }
@@ -139,9 +147,9 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)
 	unsigned long flags;
 
 	mask = ~mask;
-	local_irq_save(flags);
+	__atomic_op_irq_save(flags);
 	*addr &= mask;
-	local_irq_restore(flags);
+	__atomic_op_irq_restore(flags);
 }
 
 #define atomic_xchg(ptr, v)		(xchg(&(ptr)->counter, (v)))
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 2974bc7..6bcb1d1 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -9,6 +9,9 @@
  *  Copyright (C) 2004-2006 Ingo Molnar
  *  Copyright (C) 2004 William Lee Irwin III
  */
+
+#define __ATOMIC_NEED_RAW_IRQ_SAVE
+
 #include <linux/kallsyms.h>
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>


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