[okl4-developer] Using OKLinux to provide services

[Damien Schulz]

Hi Geoffrey,

the pagefault happens in the function dequeue_task of the Linux kernel. Any idea what could cause this problem?

01f09110 <dequeue_task>:
 1f09110:	e1a0c00d 	mov	ip, sp
 1f09114:	e92dd830 	stmdb	sp!, {r4, r5, fp, ip, lr, pc}
 1f09118:	e2804020 	add	r4, r0, #32	; 0x20
 1f0911c:	e24cb004 	sub	fp, ip, #4	; 0x4
 1f09120:	e3a02601 	mov	r2, #1048576	; 0x100000
 1f09124:	e2822c01 	add	r2, r2, #256	; 0x100
 1f09128:	e2815004 	add	r5, r1, #4	; 0x4
 1f0912c:	e5913000 	ldr	r3, [r1]                                    <-- crash
 1f09130:	e2433001 	sub	r3, r3, #1	; 0x1
 1f09134:	e5813000 	str	r3, [r1]

Thank you!
~Damien

--- glee at ok-labs.com wrote:

From: Geoffrey Lee <glee at ok-labs.com>
To: Damien Schulz <damien.schulz at 4xtc.de>
Cc: developer at okl4.org
Subject: Re: [okl4-developer] Using OKLinux to provide services
Date: Wed, 6 Aug 2008 14:23:44 +1000

On Tue, Aug 05, 2008 at 07:51:58AM -0700, Damien Schulz wrote:
> Hi there,
> 
> currently I'm implementing a service on top of OKLinux that communicates via IPC with other OKLinux instances (clients). An example how to access OKL4 services from OKLinux is already provided in the wiki pages but not how to provide services in OKLinux.
> 
> The service itself is provided by a user-mode program that reads from a procfs file. The read operation is blocked using a mutex until an IPC has been received by the server thread (in kernel mode).
> 
> But I always get the following page fault:
> waiting for lock...
> <...>
> server: Received IPC ( from = 108001, label = 12 ).
> server: producer 1 -- end
> Unhandled page fault:
>   addr=0x0/??? priv=R
>   ip=0x1e0912c, sp=1efe6ac
>   pd=0x00127240 thread=0xfc001
> 
> Has anyone an idea would could cause this page fault and how I can avoid it. I'm using OKL4 1.5.2. Below you will find the modifications to the OKLinux kernel:
> 

To debug this, you need to break into the debugger to find out which 
thread is causing the pagefault, then disassemble the relevant program
to see what it was doing at that point in time.

	-gl

> main.c:
>   int main(int argc, char **argv) {
>     <...>
>     thread_create(&ipc_thread);
>     r = L4_Set_Priority(ipc_thread, 98);
>     L4_KDB_SetThreadName(ipc_thread, "L_ipc");
>     <...>
>     L4_Start_SpIp(ipc_thread, (L4_Word_t) &ipc_stack[STACK_SIZE-1], (L4_Word_t) ipc_loop);
>     <...>
> }
> 
> ipc_loop.c:
>   unsigned long xchg_data;
>   struct semaphore PC1_w, PC1_r, PC1_m, PC2_w, PC2_r, PC2_m;
> 
>   void ipc_loop(void) {
>     L4_MsgTag_t tag;
>     L4_ThreadId_t from;
>     L4_Msg_t msg;
> 
>     init_MUTEX(&PC1_w);
>     init_MUTEX(&PC1_r);
>     down(&PC1_r);
>     init_MUTEX(&PC1_m);
> 
>     /* producer 1 begin */
>     down(&PC1_w);
>     down(&PC1_m);
> 
>     printk("server: waiting for incoming messages...\n");
>     while ( 1 ) {
>         tag = L4_Wait( &from );
>         while ( L4_IpcSucceeded( tag ) ) {
>             unsigned int label = L4_Label( tag );
>             printk( "server: received IPC ( from = %lx, label = %lx ).\n", (unsigned int)from.raw, label );
> 
>             xchg_data = label;
> 
>             /* producer 1 end */
>             up(&PC1_m);
>             up(&PC1_r);
> 
>             printk( "server: producer 1 -- end\n" );
> 
>             /* consumer 2 begin */
>             down(&PC2_r);
>             down(&PC2_m);
>     <...>
> 
> 
> procfs_module.c:
>   extern unsigned long xchg_data;
>   extern struct semaphore PC1_w, PC1_r, PC1_m, PC2_w, PC2_r, PC2_m;
> 
>   static int __init proc_init(void) {
>     init_MUTEX(&PC2_w);
>     init_MUTEX(&PC2_r);
>     down(&PC2_r);
>     init_MUTEX(&PC2_m);
>     <...>
> 
>   static int proc_server_wait_ipc( char *buf, char **start, off_t offset, int size, int *eof, void *data) {
>     printk( "waiting for lock...\n" );
>     /* consumer 1 begin */
>     down(&PC1_r);
>     down(&PC1_m);
>     printk( "recvd = %08x\n", xchg_data );
>     *((unsigned int*)buf) = xchg_data;
>     /* consumer 1 end */
>     up(&PC1_m);
>     up(&PC1_w);
> 
>     /* producer 2 begin */
>     down(&PC2_w);
>     down(&PC2_m);
>     *eof = 1;
>     return 4;
>   }
> 
> Thank you!
>  ~Damien
> 
> _______________________________________________
> Developer mailing list
> Developer at okl4.org
> https://lists.okl4.org/mailman/listinfo/developer
> 

--