Hello Gerum,
sorry for not knowing the details. But there is another question.
Is it okay to move the pointer to the arguments to the newly created task?
Isn't it possible that the task which created the new task is rescheduled?
The old task could change the value of the argument and because the new
task only holds a reference to this argument, the new task is also
affected.
Thank you
Markus
Philippe Gerum
<[EMAIL PROTECTED] An: Markus
Osterried <[EMAIL PROTECTED]>
g> Kopie:
xenomai-core@gna.org
Gesendet von: Blindkopie:
xenomai-core-bo Thema: Re:
[Xenomai-core] Arguments in psos t_start()
[EMAIL PROTECTED]
08.05.2007
16:55
Bitte antworten
an rpm
On Tue, 2007-05-08 at 16:07 +0200, Markus Osterried wrote:
> Hello Phillipe,
>
> in __t_start() in /ksrc/skins/psos+/syscall.c the pointer to the
> (user-space) tasks argument is directly used for the (kernel-space)
> t_start() call.
>
> u_long *argp;
> argp = (u_long *)__xn_reg_arg4(regs);
> return t_start((u_long)task, mode, startaddr, argp);
>
>
> I think the arguments must be copied to kernel-space, so isn't it better
to
> do it this way?
>
> u_long arg[4];
> if (!__xn_access_ok
> (curr, VERIFY_READ, __xn_reg_arg4(regs), sizeof(u_long[4])))
> return -EFAULT;
> __xn_copy_from_user(curr, arg, (void __user *)__xn_reg_arg4(regs),
> sizeof(u_long[4]));
> return t_start((u_long)task, mode, startaddr, arg);
>
Actually, we currently don't need to know anything about the task args
from kernel space, since we only have to relay their address to the task
trampoline code in src/skins/psos/task.c. However, we must not try to
access those args from kernel space. The patch below fixes this bug.
Thanks for pointing this out.
--- ksrc/skins/psos+/task.c (revision 2395)
+++ ksrc/skins/psos+/task.c (working copy)
@@ -197,9 +197,6 @@
xnmode = psos_mode_to_xeno(mode);
- for (n = 0; n < 4; n++)
- task->args[n] = targs ? targs[n] : 0;
-
task->entry = startaddr;
#if defined(__KERNEL__) && defined(CONFIG_XENO_OPT_PERVASIVE)
@@ -214,10 +211,15 @@
XNPOD_ALL_CPUS, (void
(*)(void *))startaddr, targs);
else
#endif /* __KERNEL__ && CONFIG_XENO_OPT_PERVASIVE */
+ {
+ for (n = 0; n < 4; n++)
+ task->args[n] = targs ? targs[n] : 0;
+
xnpod_start_thread(&task->threadbase,
xnmode,
(int)((mode >> 8) &
0x7),
XNPOD_ALL_CPUS,
&psostask_trampoline, task);
+ }
unlock_and_exit:
--
Philippe.
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