linux-kernel - [PATCH] lkdtm/bugs: In lkdtm_HUNG_TASK() use BUG(), not BUG

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Date: Fri, 26 Jan 2024 07:28:53 -0800
From: Douglas Anderson <dianders@...omium.org>
To: Kees Cook <keescook@...omium.org>
Cc: Douglas Anderson <dianders@...omium.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] lkdtm/bugs: In lkdtm_HUNG_TASK() use BUG(), not BUG_ON(1)

In commit edb6538da3df ("lkdtm/bugs: Adjust lkdtm_HUNG_TASK() to avoid
tail call optimization") we marked lkdtm_HUNG_TASK() as
__noreturn. The compiler gets unhappy if it thinks a __noreturn
function might return, so there's a BUG_ON(1) at the end. Any human
can see that the function won't return and the compiler can figure
that out too. Except when it can't.

The MIPS architecture defines HAVE_ARCH_BUG_ON and defines its own
version of BUG_ON(). The MIPS version of BUG_ON() is not a macro but
is instead an inline function. Apparently this prevents the compiler
from realizing that the condition to BUG_ON() is constant and that the
function will never return.

Let's change the BUG_ON(1) to just BUG(), which it should have been to
begin with. The only reason I used BUG_ON(1) to begin with was because
I was used to using WARN_ON(1) when writing test code and WARN() and
BUG() are oddly inconsistent in this manner. :-/

Fixes: edb6538da3df ("lkdtm/bugs: Adjust lkdtm_HUNG_TASK() to avoid tail call optimization")
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

 drivers/misc/lkdtm/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index d1222d3eda2f..b92767d6bdd2 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -298,7 +298,7 @@ static void __noreturn lkdtm_HUNG_TASK(void)
 {
 	set_current_state(TASK_UNINTERRUPTIBLE);
 	schedule();
-	BUG_ON(1);
+	BUG();
 }

 static volatile unsigned int huge = INT_MAX - 2;
-- 
2.43.0.429.g432eaa2c6b-goog