linux-kernel - Re: [PATCH v2 0/2] Lock and Pointer guards

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Date:   Tue, 30 May 2023 11:34:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     keescook@...omium.org, gregkh@...uxfoundation.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        ojeda@...nel.org, ndesaulniers@...gle.com, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        rcu@...r.kernel.org, tj@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH v2 0/2] Lock and Pointer guards

On Tue, May 30, 2023 at 11:23:42AM +0200, Peter Zijlstra wrote:

> Yes, it's a wee bit more involved, but I'm thinking it gives a fair
> amount of flexibility and we don't need to ret rid of
> -Wdeclaration-after-statement.

One other thing I forgot to point put; it allows things like:

	int store_fd(int fd)
	{
		ptr_guard(fdput, f) = fdget(fd);
		void *ret;
		if (!f.file)
			return -EBADF;
		ret = xa_store(&xarray, f.file->private, f);
		if (xa_is_err(ret))
			return xa_err(ret);
		f = null_ptr(fdput); // xarray now owns f
		return 0;
	}

Where we can assign null_ptr() to clear the guard and inhibit the
cleanup function to pass ownership around.