CONFIG_DESKTOP=n gives "request_module: runaway loop modprobe binfmt-464c"

[Denys Vlasenko]

On Monday 10 January 2011 08:08, Arno Steffen wrote:
> In an embedded system it is recommended to set CONFIG_DESKTOP=n.
> While busybox is working with CONFIG_DESKTOP=y, I get an error message
> while booting
> "request_module: runaway loop modprobe binfmt-464c"

464c is letters L and F. They come from this kernel code:

                if (retval != -ENOEXEC || bprm->mm == NULL) {
                        break;
#ifdef CONFIG_MODULES
                } else {
#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
                        if (printable(bprm->buf[0]) &&
                            printable(bprm->buf[1]) &&
                            printable(bprm->buf[2]) &&
                            printable(bprm->buf[3]))
                                break; /* -ENOEXEC */
                        request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
#endif
                }

ELF executables start with 0x7f,'E','L','F' bytes - that's where L and F come from.

You have ELF support compiled as a module.

modprobe is started by kernel in order to load it.
But modprobe is an ELF executable.
Kernel needs to load ELF support module for it.
modprobe is started by kernel in order to load it.
But modprobe is an ELF executable.
Kernel needs to load ELF support module for it.
modprobe is started by kernel in order to load it.
But modprobe is an ELF executable.
Kernel needs to load ELF support module for it.
modprobe is started by kernel in order to load it.
But modprobe is an ELF executable.
Kernel needs to load ELF support module for it.
modprobe is started by kernel in order to load it.
But modprobe is an ELF executable.
Kernel needs to load ELF support module for it.
At this point we trigger this:

        max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
        atomic_inc(&kmod_concurrent);
        if (atomic_read(&kmod_concurrent) > max_modprobes) {
                /* We may be blaming an innocent here, but unlikely */
                if (kmod_loop_msg++ < 5)
                        printk(KERN_ERR
                               "request_module: runaway loop modprobe %s\n",
                               module_name);
                atomic_dec(&kmod_concurrent);
                return -ENOMEM;
        }


> I searched for solution in net, but found only something regarding 32
> and 64bit OS.
> Si I have no clue, what's the problem here.
> 
> Used current busybox 1.18.1, compiled for arm.

Recompile your kernel so that ELF support is built in.

-- 
vda