[PATCH v2 2/4] cpumask: Fix invalid uniprocessor mask assumption

[Sander Vanheule]

On uniprocessor builds, any CPU mask is assumed to contain exactly one
CPU (cpu0). This assumption ignores the existence of empty masks, for
which the optimised implementations result in incorrect behaviour, and
causes the tests to fail:

[...]     # Subtest: cpumask
[...]     1..6
[...]     ok 1 - test_cpumask_weight
[...]     # test_cpumask_first: ASSERTION FAILED at lib/test_cpumask.c:35
[...]     Expected 1U <= cpumask_first(&mask_empty), but
[...]         1U == 1
[...]         cpumask_first(&mask_empty) == 0
[...]     not ok 2 - test_cpumask_first
[...]     # test_cpumask_last: ASSERTION FAILED at lib/test_cpumask.c:44
[...]     Expected ((unsigned int)1) <= cpumask_last(&mask_empty), but
[...]         ((unsigned int)1) == 1
[...]         cpumask_last(&mask_empty) == 0
[...]     not ok 3 - test_cpumask_last
[...]     # test_cpumask_next: ASSERTION FAILED at lib/test_cpumask.c:51
[...]     Expected 1U <= cpumask_next_zero(-1, ((const struct cpumask *)&__cpu_possible_mask)), but
[...]         1U == 1
[...]         cpumask_next_zero(-1, ((const struct cpumask *)&__cpu_possible_mask)) == 0
[...]     not ok 4 - test_cpumask_next
[...]     # test_cpumask_iterators: EXPECTATION FAILED at lib/test_cpumask.c:62
[...]     Expected (cpumask_weight(&mask_empty)) == (iterations), but
[...]         (cpumask_weight(&mask_empty)) == 0
[...]         (iterations) == 1
[...]     # test_cpumask_iterators: EXPECTATION FAILED at lib/test_cpumask.c:66
[...]     Expected (cpumask_weight(&mask_empty)) == (iterations), but
[...]         (cpumask_weight(&mask_empty)) == 0
[...]         (iterations) == 1
[...]     # test_cpumask_iterators: EXPECTATION FAILED at lib/test_cpumask.c:71
[...]     Expected (1U - cpumask_weight(((const struct cpumask *)&__cpu_possible_mask))) == (iterations), but
[...]         (1U - cpumask_weight(((const struct cpumask *)&__cpu_possible_mask))) == 0
[...]         (iterations) == 1
[...]     not ok 5 - test_cpumask_iterators
[...]     ok 6 - test_cpumask_iterators_builtin

Drop the incorrectly optimised code and use the generic implementations
in all cases.

Signed-off-by: Sander Vanheule <sander@xxxxxxxxxxxxx>
---
 include/linux/cpumask.h | 80 -----------------------------------------
 lib/Makefile            |  3 +-
 2 files changed, 1 insertion(+), 82 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index fe29ac7cc469..d6add0e29ef4 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
@@ -324,7 +245,6 @@ 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 81f944cd74ae..5abd7b2064f1 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
-- 
2.36.1