simple preemption debug check

PATCH New Robert Love 1 participant 1 message Apr 3, 2002 Locking primitives

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Robert Love

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2002-04-03 23:54 UTC #0 lore raw

PATCH 1/1 simple preemption debug check

Linus,

This simple check was first suggested by Andrew Morton. Pretty basic - whines if a task exits with a nonzero preempt_count value.

I put an identical check in the 2.4 preempt-kernel patch and - sure enough - it was found that XFS essentially disables preemption as it destroys data structures containing locks without first unlocking. The SGI folks are working on that.

Anyhow, its a quick and clean solution to debugging potential problems. Patch is against 2.5.7, please apply.

Robert Love

include/linux/spinlock.h +1 -1

diff -urN linux-2.5.7/include/linux/spinlock.h linux/include/linux/spinlock.h
@@ -204,7 +204,7 @@
 
 #else
 
-#define preempt_get_count()	do { } while (0)
+#define preempt_get_count()	(0)
 #define preempt_disable()	do { } while (0)
 #define preempt_enable_no_resched()	do {} while(0)
 #define preempt_enable()	do { } while (0)

kernel/exit.c +5 -0

diff -urN linux-2.5.7/kernel/exit.c linux/kernel/exit.c
@@ -492,6 +492,11 @@
 	tsk->flags |= PF_EXITING;
 	del_timer_sync(&tsk->real_timer);
 
+	if (unlikely(preempt_get_count()))
+		printk(KERN_ERR "error: %s[%d] exited with preempt_count %d\n",
+				current->comm, current->pid,
+				preempt_get_count());
+
 fake_volatile:
 #ifdef CONFIG_BSD_PROCESS_ACCT
 	acct_process(code);