[patch 08/14] syslets: x86, add create_async_thread() method

[patch 08/14] syslets: x86, add create_async_thread() method

[Ingo Molnar]

From: Ingo Molnar <mingo@elte.hu>

add the create_async_thread() way of creating kernel threads:
these threads first execute a kernel function and when they
return from it they execute user-space.

An architecture must implement this interface before it can turn
CONFIG_ASYNC_SUPPORT on.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
---
 arch/i386/kernel/entry.S     |   25 +++++++++++++++++++++++++
 arch/i386/kernel/process.c   |   31 +++++++++++++++++++++++++++++++
 include/asm-i386/processor.h |    5 +++++
 3 files changed, 61 insertions(+)

Index: linux/arch/i386/kernel/entry.S
===================================================================
--- linux.orig/arch/i386/kernel/entry.S
+++ linux/arch/i386/kernel/entry.S
@@ -996,6 +996,31 @@ ENTRY(kernel_thread_helper)
 	CFI_ENDPROC
 ENDPROC(kernel_thread_helper)
 
+ENTRY(async_thread_helper)
+	CFI_STARTPROC
+	/*
+	 * Allocate space on the stack for pt-regs.
+	 * sizeof(struct pt_regs) == 64, and we've got 8 bytes on the
+	 * kernel stack already:
+	 */
+	subl $64-8, %esp
+	CFI_ADJUST_CFA_OFFSET 64
+	movl %edx,%eax
+	push %edx
+	CFI_ADJUST_CFA_OFFSET 4
+	call *%ebx
+	addl $4, %esp
+	CFI_ADJUST_CFA_OFFSET -4
+
+	movl %eax, PT_EAX(%esp)
+
+	GET_THREAD_INFO(%ebp)
+
+	jmp syscall_exit
+	CFI_ENDPROC
+ENDPROC(async_thread_helper)
+
+
 .section .rodata,"a"
 #include "syscall_table.S"
 
Index: linux/arch/i386/kernel/process.c
===================================================================
--- linux.orig/arch/i386/kernel/process.c
+++ linux/arch/i386/kernel/process.c
@@ -352,6 +352,37 @@ int kernel_thread(int (*fn)(void *), voi
 EXPORT_SYMBOL(kernel_thread);
 
 /*
+ * This gets run with %ebx containing the
+ * function to call, and %edx containing
+ * the "args".
+ */
+extern void async_thread_helper(void);
+
+/*
+ * Create an async thread
+ */
+int create_async_thread(int (*fn)(void *), void * arg, unsigned long flags)
+{
+	struct pt_regs regs;
+
+	memset(&regs, 0, sizeof(regs));
+
+	regs.ebx = (unsigned long) fn;
+	regs.edx = (unsigned long) arg;
+
+	regs.xds = __USER_DS;
+	regs.xes = __USER_DS;
+	regs.xgs = __KERNEL_PDA;
+	regs.orig_eax = -1;
+	regs.eip = (unsigned long) async_thread_helper;
+	regs.xcs = __KERNEL_CS | get_kernel_rpl();
+	regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
+
+	/* Ok, create the new task.. */
+	return do_fork(flags, 0, &regs, 0, NULL, NULL);
+}
+
+/*
  * Free current thread data structures etc..
  */
 void exit_thread(void)
Index: linux/include/asm-i386/processor.h
===================================================================
--- linux.orig/include/asm-i386/processor.h
+++ linux/include/asm-i386/processor.h
@@ -472,6 +472,11 @@ extern void prepare_to_copy(struct task_
  */
 extern int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags);
 
+/*
+ * create an async thread:
+ */
+extern int create_async_thread(int (*fn)(void *), void * arg, unsigned long flags);
+
 extern unsigned long thread_saved_pc(struct task_struct *tsk);
 void show_trace(struct task_struct *task, struct pt_regs *regs, unsigned long *stack);
 

Re: [patch 08/14] syslets: x86, add create_async_thread() method

[Davide Libenzi]

On Thu, 15 Feb 2007, Ingo Molnar wrote:

> +ENTRY(async_thread_helper)
> +	CFI_STARTPROC
> +	/*
> +	 * Allocate space on the stack for pt-regs.
> +	 * sizeof(struct pt_regs) == 64, and we've got 8 bytes on the
> +	 * kernel stack already:
> +	 */
> +	subl $64-8, %esp
> +	CFI_ADJUST_CFA_OFFSET 64

Maybe a comment here would help in explaining why we do need space for the 
extra pt_regs (on top of the one already allocated in do_fork()) ;)
It's not immediately clear that ret_from_fork and syscall_exit will issue 
two nested RESTORE_REGS.



- Davide

Re: [patch 08/14] syslets: x86, add create_async_thread() method

[Evgeniy Polyakov]

On Thu, Feb 15, 2007 at 05:52:39PM +0100, Ingo Molnar (mingo@elte.hu) wrote:
> +/*
> + * Create an async thread
> + */
> +int create_async_thread(int (*fn)(void *), void * arg, unsigned long flags)
> +{
> +	struct pt_regs regs;
> +
> +	memset(&regs, 0, sizeof(regs));
> +
> +	regs.ebx = (unsigned long) fn;
> +	regs.edx = (unsigned long) arg;
> +
> +	regs.xds = __USER_DS;
> +	regs.xes = __USER_DS;
> +	regs.xgs = __KERNEL_PDA;
> +	regs.orig_eax = -1;
> +	regs.eip = (unsigned long) async_thread_helper;
> +	regs.xcs = __KERNEL_CS | get_kernel_rpl();
> +	regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
> +
> +	/* Ok, create the new task.. */
> +	return do_fork(flags, 0, &regs, 0, NULL, NULL);
> +}

What about complete disabling of signals and only enabling them in the
thread which returns to userspace?

-- 
	Evgeniy Polyakov