Re: 2.5.31: modules don't work at all

Andrew Morton
2002-08-12T05:23:15Z

Skip Ford wrote:
>
> ...
> > I already know that the error that trips insmod occurs at
> > in modules.c, line 831, when qm_symbols gets an error from copy_to_user():
> >
> > for (; i < mod->nsyms ; ++i, ++s, vals += 2) {
> > len = strlen(s->name)+1;
> > if (len > bufsize)
> > goto calc_space_needed;
> >
> > here------> if (copy_to_user(strings, s->name, len)
> > || __put_user(s->value, vals+0)
> > || __put_user(space, vals+1))
> > return -EFAULT;
> >
> > strings += len;
> > bufsize -= len;
> > space += len;
> > }
> >
> > The values of strings and s->name are similar in 2.5.30+preempt
> > (works) and 2.5.31+preempt (does not work). strings is 0x08______, and
> > s->name is 0xc0______.
>
> If I back out this change to arch/i386/mm/fault.c then modules
> successfully load. I have no idea if backing it out causes other
> problems though.
>
> diff -Nru a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
> --- a/arch/i386/mm/fault.c Sat Aug 10 18:42:20 2002
> +++ b/arch/i386/mm/fault.c Sat Aug 10 18:42:20 2002
> @@ -181,10 +181,10 @@
> info.si_code = SEGV_MAPERR;
>
> /*
> - * If we're in an interrupt or have no user
> - * context, we must not take the fault..
> + * If we're in an interrupt, have no user context or are running in an
> + * atomic region then we must not take the fault..
> */
> - if (in_interrupt() || !mm)
> + if (preempt_count() || !mm)
> goto no_context;
>
> down_read(&mm->mmap_sem);
>

Yes, that's the problem. qm_symbols() is performing copy_to_user()
inside lock_kernel() and that's an "atomic copy_to_user()" in 2.5.31.
But only if preempt is selected. The copy_to_user() doesn't work.

There's nothing illegal about copy_to_user() inside lock_kernel().

Linus, we can back out the preempt_count() test in there and
perform the atomic copy_*_user via a current->flags bit, or
we can do something else?