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SubjectRe: [PATCH] Make kthread_stop() not oops when passed a bad pointer
Date
On Tuesday 05 August 2008 23:55:59 Matthew Wilcox wrote:
> Make kthread_stop a little more robust against numbskulls
> like me.
>
> Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

Hi Willy,

I really do sympathize with your problem; but the quest is to figure out how
to identify it before the code is run, not to put a non-orthogonal bandaid
here which can hurt other cases.

How about a more ambitious "we've oopsed so break a mutex every 30 seconds of
waiting" patch?

> +     if (!k || IS_ERR(k))
> +             return -EINVAL;

1) There's no reason that kthread_stop is uniquely difficult to use. Why pick
on that one?

2) I know that kfree() handles NULL, but kthread_create/kthread_run never
return NULL, unlike kmalloc().

3) If we really want to pass a failed kthread_create() through kthread_stop(),
we should return PTR_ERR(k) here. But that should only be done if it made it
harder for the callers to screw up, which I don't think it does.

4) After a successful kthread_run(), kthread_stop() will always return the
value from the threadfn callback. ie. kthread_stop() doesn't ever fail. A
simple semantic, which this patch breaks.

5) Covering up programmer errors is not good policy. I dislike WARN_ON()
because an oops is much harder to miss. Painful for you, but The System
Works.

Sorry,
Rusty.
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