[PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Phil Auld]

As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
This leads to very large file sizes:

topology$ ls -l
total 0
-r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus
-r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
-r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
-r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
-r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
-r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
-r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
-r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
-r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
-r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
-r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
-r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
-r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list

Adjust the inequality to catch the case when NR_CPUS is configured
to a small value.

Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
Reported-by: feng xiangjun <fengxj325@gmail.com>
Signed-off-by: Phil Auld <pauld@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: stable@vger.kernel.org
Cc: feng xiangjun <fengxj325@gmail.com>
---
 include/linux/cpumask.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index bd047864c7ac..7b1349612d6d 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
  * cover a worst-case of every other cpu being on one of two nodes for a
  * very large NR_CPUS.
  *
- *  Use PAGE_SIZE as a minimum for smaller configurations.
+ *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
+ *  unsigned comparison to -1.
  */
-#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
+#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \
 					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
 #define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
 
-- 
2.31.1

Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Greg Kroah-Hartman]

On Tue, Sep 06, 2022 at 12:04:30PM -0400, Phil Auld wrote:
> As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
> This leads to very large file sizes:
> 
> topology$ ls -l
> total 0
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus

Yeah, lots of CPUs!  :)

> -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
> -r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
> -r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list
> 
> Adjust the inequality to catch the case when NR_CPUS is configured
> to a small value.
> 
> Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
> Reported-by: feng xiangjun <fengxj325@gmail.com>
> Signed-off-by: Phil Auld <pauld@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: stable@vger.kernel.org
> Cc: feng xiangjun <fengxj325@gmail.com>
> ---
>  include/linux/cpumask.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index bd047864c7ac..7b1349612d6d 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
>   * cover a worst-case of every other cpu being on one of two nodes for a
>   * very large NR_CPUS.
>   *
> - *  Use PAGE_SIZE as a minimum for smaller configurations.
> + *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
> + *  unsigned comparison to -1.
>   */
> -#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \
>  					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
>  #define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
>  
> -- 
> 2.31.1
> 

Nice catch.  What type of systems did you run this on to verify it will
work?

thanks,

greg k-h

Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Phil Auld]

On Tue, Sep 06, 2022 at 07:02:37PM +0200 Greg Kroah-Hartman wrote:
> On Tue, Sep 06, 2022 at 12:04:30PM -0400, Phil Auld wrote:
> > As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
> > This leads to very large file sizes:
> > 
> > topology$ ls -l
> > total 0
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus
> 
> Yeah, lots of CPUs!  :)
>

Yep, apparently things like lscpu fail with this size. 


> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list
> > 
> > Adjust the inequality to catch the case when NR_CPUS is configured
> > to a small value.
> > 
> > Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
> > Reported-by: feng xiangjun <fengxj325@gmail.com>
> > Signed-off-by: Phil Auld <pauld@redhat.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > Cc: Yury Norov <yury.norov@gmail.com>
> > Cc: stable@vger.kernel.org
> > Cc: feng xiangjun <fengxj325@gmail.com>
> > ---
> >  include/linux/cpumask.h | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > index bd047864c7ac..7b1349612d6d 100644
> > --- a/include/linux/cpumask.h
> > +++ b/include/linux/cpumask.h
> > @@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
> >   * cover a worst-case of every other cpu being on one of two nodes for a
> >   * very large NR_CPUS.
> >   *
> > - *  Use PAGE_SIZE as a minimum for smaller configurations.
> > + *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
> > + *  unsigned comparison to -1.
> >   */
> > -#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> > +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \
> >  					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
> >  #define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
> >  
> > -- 
> > 2.31.1
> > 
> 
> Nice catch.  What type of systems did you run this on to verify it will
> work?
>

Feng ran it on his 2 cpu laptop.  I ran it on my usual test bed (80 cpus) but
configured both with NR_CPUS at 8192 and at 2.

It's not really dependent on the actual system. It's a compile time config
option.  I failed to set it small when testing the first one.

The fix here is just maths :) 

With NR_CPUS == 2:

# ls -l /sys/devices/system/cpu/cpu0/topology/
total 0
-r--r--r--. 1 root root 4096 Sep  6 11:40 cluster_cpus
-r--r--r--. 1 root root 4096 Sep  6 11:40 cluster_cpus_list
-r--r--r--. 1 root root 4096 Sep  6 11:40 cluster_id
-r--r--r--. 1 root root 4096 Sep  6 11:40 core_cpus
-r--r--r--. 1 root root 4096 Sep  6 11:40 core_cpus_list
-r--r--r--. 1 root root 4096 Sep  6 11:40 core_id
-r--r--r--. 1 root root 4096 Sep  6 11:29 core_siblings
-r--r--r--. 1 root root 4096 Sep  6 11:40 core_siblings_list
...



Cheers,
Phil

> thanks,
> 
> greg k-h
> 

-- 

Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Yury Norov]

On Tue, Sep 06, 2022 at 12:04:30PM -0400, Phil Auld wrote:
> As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
> This leads to very large file sizes:
> 
> topology$ ls -l
> total 0
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
> -r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
> -r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
> -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
> -r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list
> 
> Adjust the inequality to catch the case when NR_CPUS is configured
> to a small value.
> 
> Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
> Reported-by: feng xiangjun <fengxj325@gmail.com>
> Signed-off-by: Phil Auld <pauld@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: stable@vger.kernel.org
> Cc: feng xiangjun <fengxj325@gmail.com>
> ---
>  include/linux/cpumask.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index bd047864c7ac..7b1349612d6d 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
>   * cover a worst-case of every other cpu being on one of two nodes for a
>   * very large NR_CPUS.
>   *
> - *  Use PAGE_SIZE as a minimum for smaller configurations.
> + *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
> + *  unsigned comparison to -1.
>   */
> -#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \

Maybe it would be easier to read with less braces and '>=' instead of '>'?
  #define CPUMAP_FILE_MAX_BYTES \
        (NR_CPUS * 9 / 32 >= PAGE_SIZE ? NR_CPUS * 9 / 32 - 1 : PAGE_SIZE)

Anyways, this is a good catch. If you think it doesn't worth an
update, I can take it in bitmap-for-next as-is.

>  					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
>  #define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
>  
> -- 
> 2.31.1

Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Yury Norov]

On Tue, Sep 06, 2022 at 11:09:54AM -0700, Yury Norov wrote:
> On Tue, Sep 06, 2022 at 12:04:30PM -0400, Phil Auld wrote:
> > As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
> > This leads to very large file sizes:
> > 
> > topology$ ls -l
> > total 0
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list
> > 
> > Adjust the inequality to catch the case when NR_CPUS is configured
> > to a small value.
> > 
> > Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
> > Reported-by: feng xiangjun <fengxj325@gmail.com>
> > Signed-off-by: Phil Auld <pauld@redhat.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > Cc: Yury Norov <yury.norov@gmail.com>
> > Cc: stable@vger.kernel.org
> > Cc: feng xiangjun <fengxj325@gmail.com>
> > ---
> >  include/linux/cpumask.h | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > index bd047864c7ac..7b1349612d6d 100644
> > --- a/include/linux/cpumask.h
> > +++ b/include/linux/cpumask.h
> > @@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
> >   * cover a worst-case of every other cpu being on one of two nodes for a
> >   * very large NR_CPUS.
> >   *
> > - *  Use PAGE_SIZE as a minimum for smaller configurations.
> > + *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
> > + *  unsigned comparison to -1.
> >   */
> > -#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> > +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \
> 
> Maybe it would be easier to read with less braces and '>=' instead of '>'?
>   #define CPUMAP_FILE_MAX_BYTES \
>         (NR_CPUS * 9 / 32 >= PAGE_SIZE ? NR_CPUS * 9 / 32 - 1 : PAGE_SIZE)
> 
> Anyways, this is a good catch. If you think it doesn't worth an
> update, I can take it in bitmap-for-next as-is.

Ah, I screwed in math. '>=' wouldn't work of course... 

Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Phil Auld]

On Tue, Sep 06, 2022 at 11:09:53AM -0700 Yury Norov wrote:
> On Tue, Sep 06, 2022 at 12:04:30PM -0400, Phil Auld wrote:
> > As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
> > This leads to very large file sizes:
> > 
> > topology$ ls -l
> > total 0
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
> > -r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
> > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
> > -r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list
> > 
> > Adjust the inequality to catch the case when NR_CPUS is configured
> > to a small value.
> > 
> > Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
> > Reported-by: feng xiangjun <fengxj325@gmail.com>
> > Signed-off-by: Phil Auld <pauld@redhat.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > Cc: Yury Norov <yury.norov@gmail.com>
> > Cc: stable@vger.kernel.org
> > Cc: feng xiangjun <fengxj325@gmail.com>
> > ---
> >  include/linux/cpumask.h | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > index bd047864c7ac..7b1349612d6d 100644
> > --- a/include/linux/cpumask.h
> > +++ b/include/linux/cpumask.h
> > @@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
> >   * cover a worst-case of every other cpu being on one of two nodes for a
> >   * very large NR_CPUS.
> >   *
> > - *  Use PAGE_SIZE as a minimum for smaller configurations.
> > + *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
> > + *  unsigned comparison to -1.
> >   */
> > -#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> > +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \
> 
> Maybe it would be easier to read with less braces and '>=' instead of '>'?
>   #define CPUMAP_FILE_MAX_BYTES \
>         (NR_CPUS * 9 / 32 >= PAGE_SIZE ? NR_CPUS * 9 / 32 - 1 : PAGE_SIZE)
> 
> Anyways, this is a good catch. If you think it doesn't worth an
> update, I can take it in bitmap-for-next as-is.
>

It would work as
   #define CPUMAP_FILE_MAX_BYTES  (((NR_CPUS * 9)/32 > PAGE_SIZE) \
   	   			     ? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)

Since 4097 > PAGE_SIZE and then you'd get PAGE_SIZE anyway. That is we could just
leave the 1 out of the inequality completely. 

If I recall at least some of the parens are needed to make the compiler happy.

I can resend with the above if you want.  

Cheers,
Phil

> >  					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
> >  #define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
> >  
> > -- 
> > 2.31.1
> 

-- 

Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES

[Yury Norov]

On Tue, Sep 06, 2022 at 02:57:41PM -0400, Phil Auld wrote:
> On Tue, Sep 06, 2022 at 11:09:53AM -0700 Yury Norov wrote:
> > On Tue, Sep 06, 2022 at 12:04:30PM -0400, Phil Auld wrote:
> > > As PAGE_SIZE is unsigned long, -1 > PAGE_SIZE when NR_CPUS <= 3.
> > > This leads to very large file sizes:
> > > 
> > > topology$ ls -l
> > > total 0
> > > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 core_cpus
> > > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_cpus_list
> > > -r--r--r-- 1 root root                 4096 Sep  5 10:58 core_id
> > > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 core_siblings
> > > -r--r--r-- 1 root root                 4096 Sep  5 11:59 core_siblings_list
> > > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 die_cpus
> > > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_cpus_list
> > > -r--r--r-- 1 root root                 4096 Sep  5 11:59 die_id
> > > -r--r--r-- 1 root root 18446744073709551615 Sep  5 11:59 package_cpus
> > > -r--r--r-- 1 root root                 4096 Sep  5 11:59 package_cpus_list
> > > -r--r--r-- 1 root root                 4096 Sep  5 10:58 physical_package_id
> > > -r--r--r-- 1 root root 18446744073709551615 Sep  5 10:10 thread_siblings
> > > -r--r--r-- 1 root root                 4096 Sep  5 11:59 thread_siblings_list
> > > 
> > > Adjust the inequality to catch the case when NR_CPUS is configured
> > > to a small value.
> > > 
> > > Fixes: 7ee951acd31a ("drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist")
> > > Reported-by: feng xiangjun <fengxj325@gmail.com>
> > > Signed-off-by: Phil Auld <pauld@redhat.com>
> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > > Cc: Yury Norov <yury.norov@gmail.com>
> > > Cc: stable@vger.kernel.org
> > > Cc: feng xiangjun <fengxj325@gmail.com>
> > > ---
> > >  include/linux/cpumask.h | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > > index bd047864c7ac..7b1349612d6d 100644
> > > --- a/include/linux/cpumask.h
> > > +++ b/include/linux/cpumask.h
> > > @@ -1127,9 +1127,10 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
> > >   * cover a worst-case of every other cpu being on one of two nodes for a
> > >   * very large NR_CPUS.
> > >   *
> > > - *  Use PAGE_SIZE as a minimum for smaller configurations.
> > > + *  Use PAGE_SIZE as a minimum for smaller configurations while avoiding
> > > + *  unsigned comparison to -1.
> > >   */
> > > -#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> > > +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32) > PAGE_SIZE + 1) \
> > 
> > Maybe it would be easier to read with less braces and '>=' instead of '>'?
> >   #define CPUMAP_FILE_MAX_BYTES \
> >         (NR_CPUS * 9 / 32 >= PAGE_SIZE ? NR_CPUS * 9 / 32 - 1 : PAGE_SIZE)
> > 
> > Anyways, this is a good catch. If you think it doesn't worth an
> > update, I can take it in bitmap-for-next as-is.
> >
> 
> It would work as
>    #define CPUMAP_FILE_MAX_BYTES  (((NR_CPUS * 9)/32 > PAGE_SIZE) \
>    	   			     ? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
> 
> Since 4097 > PAGE_SIZE and then you'd get PAGE_SIZE anyway. That is we could just
> leave the 1 out of the inequality completely. 
> 
> If I recall at least some of the parens are needed to make the compiler happy.
> 
> I can resend with the above if you want.  

Yes, please