linux-kernel - Re: Rust kernel policy

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Message-ID: <f4a0d359-456d-4b90-bc0f-995d26837623@p183>
Date: Thu, 20 Feb 2025 09:26:55 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Willy Tarreau <w@....eu>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Christoph Hellwig <hch@...radead.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	rust-for-linux <rust-for-linux@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	David Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
	ksummit@...ts.linux.dev
Subject: Re: Rust kernel policy

On Wed, Feb 19, 2025 at 11:33:31AM -0500, Steven Rostedt wrote:
> On Wed, 19 Feb 2025 17:15:43 +0100
> Willy Tarreau <w@....eu> wrote:
> 
> > Yeah absolutely. However I remember having faced code in the past where
> > developers had abused this "unlock on return" concept resulting in locks
> > lazily being kept way too long after an operation. I don't think this
> > will happen in the kernel thanks to reviews, but typically all the stuff
> > that's done after a locked retrieval was done normally is down outside
> > of the lock, while here for the sake of not dealing with unlocks, quite
> > a few lines were still covered by the lock for no purpose. Anyway
> > there's no perfect solution.
> 
> This was one of my concerns, and it does creep up slightly (even in my own
> use cases where I implemented them!).
> 
> But we should be encouraging the use of:
> 
> 	scoped_guard(mutex)(&my_mutex) {
> 		/* Do the work needed for for my_mutex */
> 	}

Meh...

	with_rcu() {
	}

	with_mutex(g_mutex) {
	}

	with_spin_lock(g_lock) {
	}

> Which does work out very well. And the fact that the code guarded by the
> mutex is now also indented, it makes it easier to review.

It only works only for ~1-2 indents then the code flow away :-(