Rusty Russell wrote:
> Yes, but between doing and undoing (in the failure path) someone has
> started using the module.
But how ? Don't we have only two ways of calling a module, i.e.
by symbol, or by callback ? All callbacks that might call a module
must be protected with try_module_get, right ? (*)
(*) Actually, if the registration can be revoked, and the
deregistration function does properly synchronize with on-going
callbacks, you shouldn't need try_module_get either. E.g.
del_timer_sync doesn't need to know about module owners.
So, if you make try_module_get work during initialization, and
modules don't publish their symbols before initialization is done,
there should be no problem ?
> Given we have a method of isolating a module already, it seems logical
> to use it to prevent exactly this race.
But that's mainly the symbol-unload race, considering that any call
through a function pointer requires try_module_get anyway. Without
try_module_get, there would also be callback-unload races if
callback de-registration doesn't synchronize (e.g. del_timer
vs. del_timer_sync).
By the way, it's also not so nice that there can't be
callbacks at removal, e.g.
service_unregister(...)
{
...
for_pending_requests(req) {
...
if (try_module_get(req->owner))
req->fn(req,REQUEST_CANCELLED);
else
printk(KERN_CRIT "we just dropped a request on the "
"floor, how nice\n");
...
}
...
}
Calling this from the module removal function would be
perfectly safe.
Actually ... can't you allow modules to be called until the
cleanup function has returned ?
> Unfortunately my last attempt
> assumed noone did this, and broke IDE and SCSI (hence pissing
> *everyone* off 8).
Two in one strike ain't bad ;-) Maybe we can find something that
gets rid of that pesky NFS, too, e.g. by adding
#define while if /* enforce efficient programming practices */
to linux/kernel.h, or such ;-)
- Werner
-- _________________________________________________________________________ / Werner Almesberger, Buenos Aires, Argentina wa@almesberger.net / /_http://www.almesberger.net/____________________________________________/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Sat Nov 30 2002 - 22:00:13 EST