Re: [9fans] ilock funny?

["Gorka Guardiola" <paurea@gmail.com>]

On Thu, May 29, 2008 at 3:34 AM, erik quanstrom <quanstro@quanstro.net> wrote:
> in this situation there are 128 kernel procs that all
> increment the same counter with some code
> that looks like so:
>
> void
> incref(void)
> {
>        ilock(&somelock);
>        someval++;
>        iunlock(&somelock);
> }
>
> (i realize there are probablly better ways to do this.)
> there is a similar function to decrease the value.
> other than this, there are no references to somelock.
>
> what i'm seeing is a panic with someval = 5. (gathered
> from the fact that someval is stored immediately after
> the somelock and is dumped with dumplockmem())
> and the panic message:

What you say simply cannot happen if your code was correct (the one
you are not showing us :-)).
isilock is a variable set by the lock to tainted as ilock instead of lock.
Having isilock=1 onlys happen After the lock has been acquired by someone.
The lock is checked with a tas() which I assume works because everything
is based on it.
My guess is that you have the lock uninitialized (key is not what it should be),
so key has a bogus value and that is where your problems start.
Zeroing the lock before using it should do the trick.

HTH.
--
- curiosity sKilled the cat