linux-kernel - Re: [PATCH v3 1/4] wait.[ch]: Introduce the simple waitqueue (swait) implementation

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Date:	Wed, 4 Nov 2015 13:12:44 +0100
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	<linux-kernel@...r.kernel.org>, <linux-rt-users@...r.kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 1/4] wait.[ch]: Introduce the simple waitqueue (swait)
 implementation

On 11/04/2015 11:33 AM, Thomas Gleixner wrote:
> On Tue, 20 Oct 2015, Daniel Wagner wrote:
>> +
>> +extern void swake_up(struct swait_queue_head *q);
>> +extern void swake_up_all(struct swait_queue_head *q);
>> +extern void swake_up_locked(struct swait_queue_head *q);
> 
> I intentionally named these functions swait_wake* in my initial
> implementation for two reasons:
> 
>   - typoing wake_up vs. swake_up only emits a compiler warning and does
>     not break the build

I played a bit around on this and came up with the patch below. The type
check results in an error.
    
>   - I really prefer new infrastructure to have a consistent prefix
>     which reflects the "subsystem". That's simpler to read and simpler
>     to grep for.
> 
>> +extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
>> +extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
>> +extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
>> +
>> +extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
>> +extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
> 
> Can we please go with the original names?
> 
> swait_prepare()
> swait_prepare_locked()
> swait_finish()
> swait_finish_locked()
> 
> Hmm?

I defer to Peter :)

>> +#define swait_event(wq, condition)					\
> 
> Here we have the same swait vs. wait problem as above. So either we
> come up with a slightly different name or have an explicit type check
> in __swait_event event.

What about something like this:

diff --git a/include/linux/swait.h b/include/linux/swait.h
index c1f9c62..f59369d 100644
--- a/include/linux/swait.h
+++ b/include/linux/swait.h
@@ -6,6 +6,9 @@
 #include <linux/spinlock.h>
 #include <asm/current.h>
 
+#define compiletime_assert_same_type(a, b) \
+       compiletime_assert(__same_type(a, b), "Need to match correct type");
+
 /*
  * Simple wait queues
  *
@@ -66,6 +69,7 @@ extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name
 #define init_swait_queue_head(q)                               \
        do {                                                    \
                static struct lock_class_key __key;             \
+               compiletime_assert_same_type(struct swait_queue_head *, q); \
                __init_swait_queue_head((q), #q, &__key);       \
        } while (0)
 

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