Messages in this thread Patch in this message | | | Date | Fri, 24 Sep 2010 09:24:34 -0700 | From | Greg KH <> | Subject | [46/80] percpu: fix pcpu_last_unit_cpu |
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2.6.35-stable review patch. If anyone has any objections, please let us know.
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From: Tejun Heo <tj@kernel.org>
commit 46b30ea9bc3698bc1d1e6fd726c9601d46fa0a91 upstream.
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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- mm/percpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/percpu.c +++ b/mm/percpu.c @@ -1413,9 +1413,9 @@ int __init pcpu_setup_first_chunk(const 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)
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