percpu: fix pcpu_last_unit_cpu
pcpu_first/last_unit_cpu are used to track which cpu has the first and
last units assigned. This in turn is used to determine the span of a
chunk for man/unmap cache flushes and whether an address belongs to
the first chunk or not in per_cpu_ptr_to_phys().
When the number of possible CPUs isn't power of two, a chunk may
contain unassigned units towards the end of a chunk. The logic to
determine pcpu_last_unit_cpu was incorrect when there was an unused
unit at the end of a chunk. It failed to ignore the unused unit and
assigned the unused marker NR_CPUS to pcpu_last_unit_cpu.
This was discovered through kdump failure which was caused by
malfunctioning per_cpu_ptr_to_phys() on a kvm setup with 50 possible
CPUs by CAI Qian.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: CAI Qian <caiqian@redhat.com>
Cc: stable@kernel.org
diff --git a/mm/percpu.c b/mm/percpu.c
index 58c572b..c76ef38 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1401,9 +1401,9 @@
if (pcpu_first_unit_cpu == NR_CPUS)
pcpu_first_unit_cpu = cpu;
+ pcpu_last_unit_cpu = cpu;
}
}
- pcpu_last_unit_cpu = cpu;
pcpu_nr_units = unit;
for_each_possible_cpu(cpu)