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Date: Tue, 6 Sep 2022 11:15:16 -0700 From: Yury Norov <yury.norov@...il.com> To: Phil Auld <pauld@...hat.com> Cc: linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J . Wysocki" <rafael@...nel.org>, Barry Song <21cnbao@...il.com>, Tian Tao <tiantao6@...ilicon.com>, feng xiangjun <fengxj325@...il.com>, stable@...r.kernel.org Subject: Re: [PATCH] drivers/base: Fix unsigned comparison to -1 in CPUMAP_FILE_MAX_BYTES 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@...il.com> > > Signed-off-by: Phil Auld <pauld@...hat.com> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> > > Cc: "Rafael J. Wysocki" <rafael@...nel.org> > > Cc: Yury Norov <yury.norov@...il.com> > > Cc: stable@...r.kernel.org > > Cc: feng xiangjun <fengxj325@...il.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...
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