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@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) \
> > ? (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
>
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