Messages in this thread |  | | Subject | Re: [PATCH v4 2/5] cpumask: Fix invalid uniprocessor mask assumption | From | Sander Vanheule <> | Date | Sun, 03 Jul 2022 16:17:30 +0200 |
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On Sat, 2022-07-02 at 14:42 -0700, Yury Norov wrote: > On Sat, Jul 02, 2022 at 06:08:25PM +0200, Sander Vanheule wrote: > > On uniprocessor builds, any CPU mask is assumed to contain exactly one > > CPU (cpu0). This assumption ignores the existence of empty masks, > > resulting in incorrect behaviour. > > cpumask_first_zero(), cpumask_next_zero(), and for_each_cpu_not() don't > > provide behaviour matching the assumption that a UP mask is always "1", > > and instead provide behaviour matching the empty mask. > > > > Drop the incorrectly optimised code and use the generic implementations > > in all cases. > > > > Signed-off-by: Sander Vanheule <sander@svanheule.net> > > Suggested-by: Yury Norov <yury.norov@gmail.com> >
To be honest, I was somewhat taken aback by this Suggested-by. I certainly appreciate the feedback you've provided, and I think the patch has gotten better for it, so I do want to acknowledge that. During reviews of other patches however, I haven't had a reviewer request this for suggestions that couldn't be spun off into a separate patch. If you are OK with this patch, a Reviewed-by would definitely be warranted and seems more appropriate IMHO.
Best, Sander
> > --- > > > > Notes: > > Changes since v3: > > - Add back UP-optimised cpumask_local_spread, cpumask_any_distribute, > > cpumask_any_and_distribute > > > > Changes since v1: > > - Drop UP implementations instead of trying to fix them > > > > include/linux/cpumask.h | 99 ++++++++--------------------------------- > > lib/Makefile | 3 +- > > lib/cpumask.c | 2 + > > 3 files changed, 22 insertions(+), 82 deletions(-) > > > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > > index fe29ac7cc469..7fbef41b3093 100644 > > --- a/include/linux/cpumask.h > > +++ b/include/linux/cpumask.h > > @@ -116,85 +116,6 @@ static __always_inline unsigned int cpumask_check(unsigned int cpu) > > return cpu; > > } > > > > -#if NR_CPUS == 1 > > -/* Uniprocessor. Assume all masks are "1". */ > > -static inline unsigned int cpumask_first(const struct cpumask *srcp) > > -{ > > - return 0; > > -} > > - > > -static inline unsigned int cpumask_first_zero(const struct cpumask *srcp) > > -{ > > - return 0; > > -} > > - > > -static inline unsigned int cpumask_first_and(const struct cpumask *srcp1, > > - const struct cpumask *srcp2) > > -{ > > - return 0; > > -} > > - > > -static inline unsigned int cpumask_last(const struct cpumask *srcp) > > -{ > > - return 0; > > -} > > - > > -/* Valid inputs for n are -1 and 0. */ > > -static inline unsigned int cpumask_next(int n, const struct cpumask *srcp) > > -{ > > - return n+1; > > -} > > - > > -static inline unsigned int cpumask_next_zero(int n, const struct cpumask *srcp) > > -{ > > - return n+1; > > -} > > - > > -static inline unsigned int cpumask_next_and(int n, > > - const struct cpumask *srcp, > > - const struct cpumask *andp) > > -{ > > - return n+1; > > -} > > - > > -static inline unsigned int cpumask_next_wrap(int n, const struct cpumask *mask, > > - int start, bool wrap) > > -{ > > - /* cpu0 unless stop condition, wrap and at cpu0, then nr_cpumask_bits */ > > - return (wrap && n == 0); > > -} > > - > > -/* cpu must be a valid cpu, ie 0, so there's no other choice. */ > > -static inline unsigned int cpumask_any_but(const struct cpumask *mask, > > - unsigned int cpu) > > -{ > > - return 1; > > -} > > - > > -static inline unsigned int cpumask_local_spread(unsigned int i, int node) > > -{ > > - return 0; > > -} > > - > > -static inline int cpumask_any_and_distribute(const struct cpumask *src1p, > > - const struct cpumask *src2p) { > > - return cpumask_first_and(src1p, src2p); > > -} > > - > > -static inline int cpumask_any_distribute(const struct cpumask *srcp) > > -{ > > - return cpumask_first(srcp); > > -} > > - > > -#define for_each_cpu(cpu, mask) \ > > - for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask) > > -#define for_each_cpu_not(cpu, mask) \ > > - for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask) > > -#define for_each_cpu_wrap(cpu, mask, start) \ > > - for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask, (void)(start)) > > -#define for_each_cpu_and(cpu, mask1, mask2) \ > > - for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask1, (void)mask2) > > -#else > > /** > > * cpumask_first - get the first cpu in a cpumask > > * @srcp: the cpumask pointer > > @@ -260,10 +181,29 @@ static inline unsigned int cpumask_next_zero(int n, const struct cpumask > > *srcp) > > > > int __pure cpumask_next_and(int n, const struct cpumask *, const struct cpumask *); > > int __pure cpumask_any_but(const struct cpumask *mask, unsigned int cpu); > > + > > +#if NR_CPUS == 1 > > +/* Uniprocessor: there is only one valid CPU */ > > +static inline unsigned int cpumask_local_spread(unsigned int i, int node) > > +{ > > + return 0; > > +} > > + > > +static inline int cpumask_any_and_distribute(const struct cpumask *src1p, > > + const struct cpumask *src2p) { > > + return cpumask_first_and(src1p, src2p); > > +} > > + > > +static inline int cpumask_any_distribute(const struct cpumask *srcp) > > +{ > > + return cpumask_first(srcp); > > +} > > +#else > > unsigned int cpumask_local_spread(unsigned int i, int node); > > int cpumask_any_and_distribute(const struct cpumask *src1p, > > const struct cpumask *src2p); > > int cpumask_any_distribute(const struct cpumask *srcp); > > +#endif /* NR_CPUS */ > > > > /** > > * for_each_cpu - iterate over every cpu in a mask > > @@ -324,7 +264,6 @@ extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, > > bool > > for ((cpu) = -1; \ > > (cpu) = cpumask_next_and((cpu), (mask1), (mask2)), \ > > (cpu) < nr_cpu_ids;) > > -#endif /* SMP */ > > > > #define CPU_BITS_NONE \ > > { \ > > diff --git a/lib/Makefile b/lib/Makefile > > index f99bf61f8bbc..bcc7e8ea0cde 100644 > > --- a/lib/Makefile > > +++ b/lib/Makefile > > @@ -34,10 +34,9 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \ > > is_single_threaded.o plist.o decompress.o kobject_uevent.o \ > > earlycpio.o seq_buf.o siphash.o dec_and_lock.o \ > > nmi_backtrace.o nodemask.o win_minmax.o memcat_p.o \ > > - buildid.o > > + buildid.o cpumask.o > > > > lib-$(CONFIG_PRINTK) += dump_stack.o > > -lib-$(CONFIG_SMP) += cpumask.o > > > > lib-y += kobject.o klist.o > > obj-y += lockref.o > > diff --git a/lib/cpumask.c b/lib/cpumask.c > > index a971a82d2f43..b9728513a4d4 100644 > > --- a/lib/cpumask.c > > +++ b/lib/cpumask.c > > @@ -192,6 +192,7 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) > > } > > #endif > > > > +#if NR_CPUS > 1 > > /** > > * cpumask_local_spread - select the i'th cpu with local numa cpu's first > > * @i: index number > > @@ -279,3 +280,4 @@ int cpumask_any_distribute(const struct cpumask *srcp) > > return next; > > } > > EXPORT_SYMBOL(cpumask_any_distribute); > > +#endif /* NR_CPUS */ > > -- > > 2.36.1
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