[PATCH] s390: Fix perf event init

[Paul Burton <paul.burton@imgtec.com>]

Commit c311c797998c ("cpumask: make "nr_cpumask_bits" unsigned")
modified cpumsf_pmu_event_init() to cast the struct perf_event cpu field
to an unsigned integer before it is compared with nr_cpumask_bits. This
is broken because the cpu field may be -1 for events which follow a
process rather than being affine to a particular CPU. When this is the
case the cast to an unsigned int results in a value equal to ULONG_MAX,
which is always greater than nr_cpumask_bits so we always fail
cpumsf_pmu_event_init() and return -ENODEV.

The check against nr_cpumask_bits seems nonsensical anyway, so this
patch simply removes it. The cpu field is going to either be 0 or a
valid CPU number. Comparing it with nr_cpumask_bits is effectively
checking that it's a valid cpu number, but it seems safe to rely on the
core perf events code to ensure that's the case.

The end result is that this fixes use of perf when not constraining
events to a particular CPU, and fixes the "perf list hw" command which
fails to list any events without this.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: c311c797998c ("cpumask: make "nr_cpumask_bits" unsigned")
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: stable <stable@vger.kernel.org> # v4.12+

---
This patch is purely speculative, based upon fixing perf on MIPS
following the offending commit c311c797998c ("cpumask: make
"nr_cpumask_bits" unsigned") which made the same change to both MIPS &
s390. I leave it to s390 developers to verify whether this affects them
in the same way as it affected MIPS thus whether this fix is correct
there too.

Thanks,
    Paul

 arch/s390/kernel/perf_cpum_sf.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index c1bf75ffb875..cc570143f245 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -823,8 +823,7 @@ static int cpumsf_pmu_event_init(struct perf_event *event)
 	}
 
 	/* Check online status of the CPU to which the event is pinned */
-	if ((unsigned int)event->cpu >= nr_cpumask_bits ||
-	    (event->cpu >= 0 && !cpu_online(event->cpu)))
+	if (event->cpu >= 0 && !cpu_online(event->cpu))
 		return -ENODEV;
 
 	/* Force reset of idle/hv excludes regardless of what the
-- 
2.14.1