Re: [PATCH] BUG(): sched.c: Line 944

[Robert Love]

On Tue, 2002-09-17 at 04:12, Robert Love wrote:

> +	if (unlikely(!kernel_locked()))
> +		tsk->lock_depth = -2;

Eh, this should be likely()...

	Robert Love

diff -urN linux-2.5.35/include/asm-i386/hardirq.h linux/include/asm-i386/hardirq.h
--- linux-2.5.35/include/asm-i386/hardirq.h	Sun Sep 15 22:18:46 2002
+++ linux/include/asm-i386/hardirq.h	Tue Sep 17 03:20:00 2002
@@ -77,7 +77,8 @@
 #define irq_enter()		(preempt_count() += HARDIRQ_OFFSET)
 
 #if CONFIG_PREEMPT
-# define in_atomic()	(preempt_count() != kernel_locked())
+# define in_atomic() \
+	((preempt_count() & ~PREEMPT_ACTIVE) != (current->lock_depth != -1))
 # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
 #else
 # define in_atomic()	(preempt_count() != 0)
diff -urN linux-2.5.35/kernel/exit.c linux/kernel/exit.c
--- linux-2.5.35/kernel/exit.c	Tue Sep 17 03:18:53 2002
+++ linux/kernel/exit.c	Tue Sep 17 03:55:12 2002
@@ -637,6 +637,21 @@
 	preempt_disable();
 	if (current->exit_signal == -1)
 		release_task(current);
+
+	/*
+	 * This little bit of genius comes from the twisted mind of Linus.
+	 * We need exit() to be atomic but we also want a debugging check
+	 * in schedule() to whine if we are atomic.  The wickedness is in
+	 * these rules:
+	 *	- task->lock_depth = -2 means "validly nonpreemptable"
+	 * 	- task->lock_depth = -1 means "BKL not held"
+         * 	- task->lock_depth >= 0 means "BKL held"
+	 * release_kernel_lock and kernel_locked() check >=0, and
+	 * in_atomic() checks != -1... the "fake BKL" will "cancel out"
+	 * the preempt_disable() above and the world is happy.
+	 */
+	if (likely(!kernel_locked()))
+		tsk->lock_depth = -2;
 	schedule();
 	BUG();
 /*
diff -urN linux-2.5.35/kernel/sched.c linux/kernel/sched.c
--- linux-2.5.35/kernel/sched.c	Sun Sep 15 22:18:24 2002
+++ linux/kernel/sched.c	Tue Sep 17 03:50:04 2002
@@ -940,8 +940,10 @@
 	struct list_head *queue;
 	int idx;
 
-	if (unlikely(in_atomic()))
-		BUG();
+	if (unlikely(in_atomic())) {
+		printk(KERN_ERR "error: scheduling while non-atomic!\n");
+		dump_stack();
+	}
 
 #if CONFIG_DEBUG_HIGHMEM
 	check_highmem_ptes();
@@ -959,7 +961,7 @@
 	 * if entering off of a kernel preemption go straight
 	 * to picking the next task.
 	 */
-	if (unlikely(preempt_count() & PREEMPT_ACTIVE))
+	if (unlikely(preempt_count() == PREEMPT_ACTIVE))
 		goto pick_next_task;
 
 	switch (prev->state) {