[PATCH] simple preemption debug check

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

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index cd7428798399f408e0c7160fd8426ed91afa6361..a78cd80f4ab638bb7f839ee74d8731b92fc51e67 100644 (file)
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -204,7 +204,7 @@ do { \
 
 #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)

diff --git a/kernel/exit.c b/kernel/exit.c
index d1a6b145161907472fc11bd46b09d4ddee7a225e..96472474ada781fb43f49d8fa5e066ae7ad5fe1f 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -490,6 +490,11 @@ NORET_TYPE void do_exit(long code)
        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:
        acct_process(code);
        __exit_mm(tsk);