linux-kernel - Re: [PATCH] iommu: Convert unreachable() to BUG()

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Message-ID: <20250327123718.GB31358@noisy.programming.kicks-ass.net>
Date: Thu, 27 Mar 2025 13:37:18 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, Randy Dunlap <rdunlap@...radead.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] iommu: Convert unreachable() to BUG()

On Wed, Mar 26, 2025 at 10:28:46PM -0700, Josh Poimboeuf wrote:
> Bare unreachable() should be avoided as it generates undefined behavior,
> e.g. falling through to the next function.  Use BUG() instead so the
> error is defined.

Right; I did a pass like this a while ago and thought I'd removed all
unreachable() abuse.

Compilers see this as a clue to just stop code-gen. Very bad behaviour
if you ever actually get there. BUG() at the very least stops the kernel
dead, instead of continuing to run random code that comes after.