Re: [patch 2/6] epoll keyed wakeups v2 - introduce new *_poll() wakeup macros

On Tue, 3 Feb 2009, Andrew Morton wrote:

On Tue, 3 Feb 2009 11:20:46 -0800 (PST)
Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote:

On Tue, 3 Feb 2009, Davide Libenzi wrote:

On Tue, 3 Feb 2009, Andrew Morton wrote:

On Sun, 01 Feb 2009 12:04:23 -0800 Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote:

+#define wake_up_nested_poll(x, m, s) \
+do { \
+ unsigned long flags; \
+ \
+ spin_lock_irqsave_nested(&(x)->lock, flags, (s)); \
+ wake_up_locked_poll(x, m); \
+ spin_unlock_irqrestore(&(x)->lock, flags); \
+} while (0)

I had to go and find the callsite to work out the type of `x' :(

- this macro can be passed the address of any structure which has a
`spinlock_t lock;' in it, which seems strange.

- It references its first arg three times.

Is there any reason why we can't implement this in C?

I don't see any reason why these two couldn't be normal functions (I
just referenced wake_up_nested(), that was a macro in the first place).

Actually reading the comments helps :) It triggers an include-hell, if you
make them inline. Since they're lockdep debug thingies, I think it's kinda
wasted turn them into non-inline real functions, so they'd better remain
macros IMO.


ho hum. I think it'd be worth at least renaming the arguments to
something less daft, for readability reasons.

One could also do

do {
wait_queue_head_t *__wqh = x;
<use __wqh>
}

which would provide typechecking of the first arg (so people can no
longer "pass the address of any structure which has a `spinlock_t
lock;' in it") and which fixes the multiple-references-to-an-argument
issue.

OK, you've got my arg-rename bits already. Another version using a
typecheck() in there? Or you prefer the explicit instantiation?


- Davide


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