Re: [PATCH 01/12] lockdep: syscall exit check

[Peter Zijlstra]

On Fri, 2007-09-28 at 14:03 +0200, Heiko Carstens wrote:
> > +void lockdep_sys_exit(void)
> > +{
> > +	struct task_struct *curr = current;
> > +
> > +	if (unlikely(curr->lockdep_depth)) {
> > +		if (!debug_locks_off())
> > +			return;
> > +		printk("\n========================================\n");
> > +		printk(  "[ BUG: lock held at syscall exit time! ]\n");
> > +		printk(  "----------------------------------------\n");
> > +		printk("%s/%d is leaving the kernel with locks still held!\n",
> > +				curr->comm, curr->pid);
> > +		lockdep_print_held_locks(curr);
> > +	}
> > +}
> 
> By the way, the s390 patch I just posted also checks if we hold any locks
> when returning from interrupt context to user space. Maybe the above text
> could be changed to "lock held when returning to user space" ?

Good idea, I'll look at doing the same for i386/x86_64. Traps (page
faults) would also make sense I guess.

---

Subject: lockdep: syscall exit check

Provide a check to validate that we do not hold any locks when switching
back to user-space.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
 include/linux/lockdep.h |    2 ++
 kernel/lockdep.c        |   16 ++++++++++++++++
 2 files changed, 18 insertions(+)

Index: linux-2.6/include/linux/lockdep.h
===================================================================
--- linux-2.6.orig/include/linux/lockdep.h
+++ linux-2.6/include/linux/lockdep.h
@@ -238,6 +238,7 @@ extern void lockdep_info(void);
 extern void lockdep_reset(void);
 extern void lockdep_reset_lock(struct lockdep_map *lock);
 extern void lockdep_free_key_range(void *start, unsigned long size);
+extern void lockdep_sys_exit(void);
 
 extern void lockdep_off(void);
 extern void lockdep_on(void);
@@ -317,6 +318,7 @@ static inline void lockdep_on(void)
 # define INIT_LOCKDEP
 # define lockdep_reset()		do { debug_locks = 1; } while (0)
 # define lockdep_free_key_range(start, size)	do { } while (0)
+# define lockdep_sys_exit() 			do { } while (0)
 /*
  * The class key takes no space if lockdep is disabled:
  */
Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c
+++ linux-2.6/kernel/lockdep.c
@@ -3199,3 +3199,19 @@ void debug_show_held_locks(struct task_s
 }
 
 EXPORT_SYMBOL_GPL(debug_show_held_locks);
+
+void lockdep_sys_exit(void)
+{
+	struct task_struct *curr = current;
+
+	if (unlikely(curr->lockdep_depth)) {
+		if (!debug_locks_off())
+			return;
+		printk("\n================================================\n");
+		printk(  "[ BUG: lock held when returning to user space! ]\n");
+		printk(  "------------------------------------------------\n");
+		printk("%s/%d is leaving the kernel with locks still held!\n",
+				curr->comm, curr->pid);
+		lockdep_print_held_locks(curr);
+	}
+}

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