From 46b30ea9bc3698bc1d1e6fd726c9601d46fa0a91 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 21 Sep 2010 07:57:19 +0200 Subject: [PATCH] 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 Reported-by: CAI Qian Cc: stable@kernel.org --- mm/percpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/percpu.c b/mm/percpu.c index 58c572b18b07..c76ef3891e0d 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1401,9 +1401,9 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai, 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) -- 2.20.1