lkml.org 
[lkml]   [2008]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: Module loading/unloading and "The Stop Machine"
Date
On Friday 22 February 2008 22:53:50 Andi Kleen wrote:
> Max Krasnyanskiy <maxk@qualcomm.com> writes:
> > static struct module *load_module(void __user *umod,
> > unsigned long len,
> > const char __user *uargs)
> > {
> > ...
> >
> > /* Now sew it into the lists so we can get lockdep and oops
> > * info during argument parsing. Noone should access us, since
> > * strong_try_module_get() will fail. */
> > stop_machine_run(__link_module, mod, NR_CPUS);
> > ...
> > }
>
> Wow you found some really bad code. I bet it wouldn't be that
> difficult to fix the code to allow oops safe list insertion
> without using the big stop machine overkill hammer.

Yes it's overkill and it's becoming more noticable with larger machines.
(Also, stop_machine is heavier than it should be, Kathy is working on fixing
that though).

Most obvious is to add __ "lockless, but I'm in trouble anyway" accessors, but
last I looked they'd have to be plumbed through a fair bit of code.

From a quick reading of the code, a lockless add is possible, but it's fragile
if one of the readers does something more complex in future.

Thanks,
Rusty.



\
 
 \ /
  Last update: 2008-03-04 02:25    [from the cache]
©2003-2011 Jasper Spaans