linux-kernel - Re: [RFC PATCH v2] cleanup: Add cond

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Date: Tue, 30 Jan 2024 18:55:23 +0100
From: "Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>
To: linux-kernel@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
 Dan Williams <dan.j.williams@...el.com>, Ira Weiny <ira.weiny@...el.com>
Subject: Re: [RFC PATCH v2] cleanup: Add cond_guard() to conditional guards

On Tuesday, 30 January 2024 18:02:09 CET Dan Williams wrote:
> Fabio M. De Francesco wrote:

[skip}

> > 
> > @@ -165,6 +174,10 @@ static inline class_##_name##_t
> > class_##_name##ext##_constructor(_init_args) \> 
> >  #define __guard_ptr(_name) class_##_name##_lock_ptr
> > 
> > +#define cond_guard(_name, args...) \
> > +	CLASS(_name, scope)(args); \
> > +	if (!__guard_ptr(_name)(&scope))
> 
> This needs to protect against being used within another if () block.
> Imagine a case of:
> 
>     if (...) {
>     	cond_guard(...);
> 	    <statement>
>     } else if (...)

Could it be made clear in the documentation that cond_guard() shouldn't be 
misused as you showed above? 

Actually, I don't know how effective the documentation can be in avoiding 
incorrect use of cond_guard().

Fabio

> ...does that "else if" belong to the first "if ()" or the hidden one
> inside the macro?
> 
> You can steal the embedded "if ()" trick from scoped_cond_guard() and do
> something like (untested):
> 
> #define cond_guard(_name, _fail, args...) \
> 	CLASS(_name, scope)(args); \
> 	if (!__guard_ptr(_name)(&scope)) _fail; else /* pass */;