Messages in this thread | | | From | Rusty Russell <> | Subject | Re: Module loading/unloading and "The Stop Machine" | Date | Tue, 4 Mar 2008 12:21:05 +1100 |
| |
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.
| |