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

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Date: Tue, 30 Jan 2024 10:43:19 -0800
From: Ira Weiny <ira.weiny@...el.com>
To: Dan Williams <dan.j.williams@...el.com>, "Fabio M. De Francesco"
	<fabio.maria.de.francesco@...ux.intel.com>, <linux-kernel@...r.kernel.org>
CC: "Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>, "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

Dan Williams wrote:
> Fabio M. De Francesco wrote:
> > Add cond_guard() to conditional guards.
> > 
> > cond_guard() is used for the _interruptible(), _killable(), and _try
> > versions of locks. It expects a block where the failure can be handled
> > (e.g., calling printk() and returning -EINTR in case of failure).
> > 
> > As the other guards, it avoids to open code the release of the lock
> > after a goto to an 'out' label.
> > 
> > This remains an RFC because Dan suggested a slightly different syntax:
> > 
> > 	if (cond_guard(...))
> > 		return -EINTR;
> > 
> > But the scoped_cond_guard() macro omits the if statement:
> > 
> >     	scoped_cond_guard (...) {
> >     	}
> > 
> > Thus define cond_guard() similarly to scoped_cond_guard() but with a block
> > to handle the failure case:
> > 
> > 	cond_guard(...)
> > 		return -EINTR;
> 
> That's too subtle for me, because of the mistakes that can be made with
> brackets how about a syntax like:
> 
>  	cond_guard(..., return -EINTR, ...)
> 
> ...to make it clear what happens if the lock acquisition fails without
> having to remember there is a hidden incomplete "if ()" statement in
> that macro? More below...

I sympathize with the hidden "if" being confusing but there is already
precedent in the current *_guard macros.  So I'd like to know if Peter has
an opinion.

Ira