linux-kernel - Re: [PATCH] x86: mmiotrace: Use cpumask_available for cpumask_var

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Message-ID: <CA+icZUUTEEZww3qT0jfFP0ZgUPXoF1_uOHMT4ZecrQxumE1Zmg@mail.gmail.com>
Date:   Wed, 8 Apr 2020 23:12:43 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Karol Herbst <karolherbst@...il.com>,
        Pekka Paalanen <ppaalanen@...il.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, nouveau@...ts.freedesktop.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] x86: mmiotrace: Use cpumask_available for cpumask_var_t variables

On Wed, Apr 8, 2020 at 10:53 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> When building with Clang + -Wtautological-compare and
> CONFIG_CPUMASK_OFFSTACK unset:
>

Hi Nathan,

thanks for the quick patch.

I can confirm I have no CONFIG_CPUMASK_OFFSTACK set.

Regards,
- Sedat -


> arch/x86/mm/mmio-mod.c:375:6: warning: comparison of array 'downed_cpus'
> equal to a null pointer is always false [-Wtautological-pointer-compare]
>         if (downed_cpus == NULL &&
>             ^~~~~~~~~~~    ~~~~
> arch/x86/mm/mmio-mod.c:405:6: warning: comparison of array 'downed_cpus'
> equal to a null pointer is always false [-Wtautological-pointer-compare]
>         if (downed_cpus == NULL || cpumask_weight(downed_cpus) == 0)
>             ^~~~~~~~~~~    ~~~~
> 2 warnings generated.
>
> Commit f7e30f01a9e2 ("cpumask: Add helper cpumask_available()") added
> cpumask_available to fix warnings of this nature. Use that here so that
> clang does not warn regardless of CONFIG_CPUMASK_OFFSTACK's value.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/982
> Reported-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/x86/mm/mmio-mod.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/mmio-mod.c b/arch/x86/mm/mmio-mod.c
> index 109325d77b3e..43fd19b3f118 100644
> --- a/arch/x86/mm/mmio-mod.c
> +++ b/arch/x86/mm/mmio-mod.c
> @@ -372,7 +372,7 @@ static void enter_uniprocessor(void)
>         int cpu;
>         int err;
>
> -       if (downed_cpus == NULL &&
> +       if (!cpumask_available(downed_cpus) &&
>             !alloc_cpumask_var(&downed_cpus, GFP_KERNEL)) {
>                 pr_notice("Failed to allocate mask\n");
>                 goto out;
> @@ -402,7 +402,7 @@ static void leave_uniprocessor(void)
>         int cpu;
>         int err;
>
> -       if (downed_cpus == NULL || cpumask_weight(downed_cpus) == 0)
> +       if (!cpumask_available(downed_cpus) || cpumask_weight(downed_cpus) == 0)
>                 return;
>         pr_notice("Re-enabling CPUs...\n");
>         for_each_cpu(cpu, downed_cpus) {
>
> base-commit: ae46d2aa6a7fbe8ca0946f24b061b6ccdc6c3f25
> --
> 2.26.0
>