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@xxxxxxxxx>
> > > Signed-off-by: Phil Auld <pauld@xxxxxxxxxx>
> > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> > > Cc: Yury Norov <yury.norov@xxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Cc: feng xiangjun <fengxj325@xxxxxxxxx>
> > > ---
> > > 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
