Nouveau - May 2020 - [PATCH] x86: mmiotrace: Use cpumask_available for cpumask_var_t variables

When building with Clang + -Wtautological-compare and
CONFIG_CPUMASK_OFFSTACK unset:

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 at gmail.com>
Signed-off-by: Nathan Chancellor <natechancellor at gmail.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

On Wed, Apr 8, 2020 at 10:53 PM Nathan Chancellor
<natechancellor at gmail.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 at gmail.com>
> Signed-off-by: Nathan Chancellor <natechancellor at gmail.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
>

On Wed, Apr 8, 2020 at 11:12 PM Sedat Dilek <sedat.dilek at gmail.com>
wrote:
>
> On Wed, Apr 8, 2020 at 10:53 PM Nathan Chancellor
> <natechancellor at gmail.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.
>
Feel free to add appropriate credits:

   Tested-by: Sedat Dilek <sedat.dilek at gmail.com>

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 at gmail.com>
> > Signed-off-by: Nathan Chancellor <natechancellor at gmail.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
> >

On Wed,  8 Apr 2020 13:53:23 -0700
Nathan Chancellor <natechancellor at gmail.com> wrote:
> When building with Clang + -Wtautological-compare and
> CONFIG_CPUMASK_OFFSTACK unset:
> 
> 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 at gmail.com>
> Signed-off-by: Nathan Chancellor <natechancellor at gmail.com>
> ---
> 
Acked-by: Steven Rostedt (VMware) <rostedt at goodmis.org>

-- Steve

On Wed, Apr 08, 2020 at 01:53:23PM -0700, Nathan Chancellor
wrote:
> When building with Clang + -Wtautological-compare and
> CONFIG_CPUMASK_OFFSTACK unset:
> 
> 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 at gmail.com>
> Signed-off-by: Nathan Chancellor <natechancellor at gmail.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
> 
Gentle ping for acceptance, I am not sure who should take this.

Cheers,
Nathan

On Mon, May 18, 2020 at 2:31 AM Nathan Chancellor
<natechancellor at gmail.com> wrote:
>
> On Wed, Apr 08, 2020 at 01:53:23PM -0700, Nathan Chancellor wrote:
> > When building with Clang + -Wtautological-compare and
> > CONFIG_CPUMASK_OFFSTACK unset:
> >
> > 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 at gmail.com>
> > Signed-off-by: Nathan Chancellor <natechancellor at gmail.com>
Thanks for the patch, sorry I'm falling behind on code review!
Reviewed-by: Nick Desaulniers <ndesaulniers at google.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
> >
>
> Gentle ping for acceptance, I am not sure who should take this.
Looks like Steven or Ingo are the listed maintainers for MMIOTRACE?

-- 
Thanks,
~Nick Desaulniers