pdflush can't exit

[Hideo S. <sa...@de...>]

Hi Paul,

When I run a preemptive kernel-2.6.20 for SH7780, a created kthread(pdflush) can not exit by do_exit() in kernel_thread_helper. I think that the created kthread should have a room for 'struct pt_regs' space on the stack top, because __switch_to() will refer to the space as follows using 'regs = task_pt_regs(prev)' and next condition may be true.

struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *next)
{
#if defined(CONFIG_SH_FPU)
	unlazy_fpu(prev, task_pt_regs(prev));
#endif

#ifdef CONFIG_PREEMPT
	{
		unsigned long flags;
		struct pt_regs *regs;

		local_irq_save(flags);
		regs = task_pt_regs(prev);
		if (user_mode(regs) && regs->regs[15] >= 0xc0000000) {
			int offset = (int)regs->regs[15];

			/* Reset stack pointer: clear critical region mark */
			regs->regs[15] = regs->regs[1];
			if (regs->pc < regs->regs[0])
				/* Go to rewind point */
				regs->pc = regs->regs[0] + offset;
		}

I think that the following patch can avoid this problem.

--- arch/sh/kernel/process.c2	Mon Feb  5 18:52:29 2007
+++ arch/sh/kernel/process.c	Mon Feb 26 12:35:17 2007
@@ -270,20 +270,20 @@ int copy_thread(int nr, unsigned long cl
 
 	childregs = task_pt_regs(p);
 	*childregs = *regs;
 
 	if (user_mode(regs)) {
 		childregs->regs[15] = usp;
 		ti->addr_limit = USER_DS;
 	} else {
-		childregs->regs[15] = (unsigned long)task_stack_page(p) + THREAD_SIZE;
+		childregs->regs[15] = (unsigned long)childregs;
 		ti->addr_limit = KERNEL_DS;
 	}
-        if (clone_flags & CLONE_SETTLS) {
+	if (clone_flags & CLONE_SETTLS) {
 		childregs->gbr = childregs->regs[0];
 	}
 	childregs->regs[0] = 0; /* Set return value for child */
 
 	p->thread.sp = (unsigned long) childregs;
 	p->thread.pc = (unsigned long) ret_from_fork;
 
 	p->thread.ubc_pc = 0;