From: Tejun Heo <[email protected]> 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 <[email protected]> Reported-by: CAI Qian <[email protected]> Signed-off-by: Paul Gortmaker <[email protected]> --- mm/percpu.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index 6e09741..717cc6e 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1750,9 +1750,9 @@ 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) -- 1.7.3.3 _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
