Re: [PATCH] Detect and warn on atomic_inc/atomic_dec wrapping around

Andrew Morton
2009-04-30T21:48:47Z

On Thu, 30 Apr 2009 19:39:50 +0530
Nikanth Karthikesan <knikanth@novell.com> wrote:

>

If I had a dollar for each wordwrapped patch I get sent...

> Detect and warn on atomic_inc/atomic_dec overflow.
>
> Add a debug option to detect and warn when the 32-bit atomic_t overflows
> during atomic_inc and atomic_dec.
>

OK.

I'll beef the changelog up a bit - this one is wimpy.

The question is: do we put this in mainline? I guess we might as well
give it a shot. It may well find bugs and it might also trigger false
positives. We can then fix the bugs and decide whether the false
positives warrant reverting it again, all very easy.

> +#include <asm/bug.h>

checkpatch says

WARNING: Use #include <linux/bug.h> instead of <asm/bug.h>
#215: FILE: include/asm-generic/atomic.h:11:
+#include <asm/bug.h>

Was this an oversight, or did you try using linux/bug.h and discovered
some problem?

> index 812c282..773c1a4 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -17,6 +17,17 @@ config ENABLE_WARN_DEPRECATED
> Disable this to suppress the "warning: 'foo' is deprecated
> (declared at kernel/power/somefile.c:1234)" messages.
>
> +config HAVE_ARCH_DEBUG_ATOMIC
> + bool
> +
> +config ENABLE_WARN_ATOMIC_INC_WRAP
> + bool "Enable warning on atomic_inc()/atomic_dec() wrap"
> + depends on HAVE_ARCH_DEBUG_ATOMIC
> + default y
> + help
> + Enable printing a warning when atomic_inc() or atomic_dec()
> + operation wraps around the 32-bit value.
> +

Yes, I agree with `default y' for now. But we might want to turn it
off again later. Adding that WARN to every atomic_inc/atomic_dec site
must do terrible things to the kernel text footprint.

Of course, if we make if `default y' for a while and then switch it to
`default n', the `y' state will linger for a very long time in all the
kernel developers' .configs. Good! Very sneaky.