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Subject[PATCH] Fixed division by zero bug in kernel/padata.c
From
 When boot CPU(typically CPU #0) is excluded from padata cpumask and
user enters halt command from console, kernel faults on division by zero;
This occurs because during the halt kernel shuts down each non-boot CPU one
by one and after it shuts down the last CPU that is set in the padata cpumask,
the only working CPU in the system is a boot CPU(#0) and it's the only CPU that
is set in the cpu_active_mask. Hence when padata_cpu_callback calls
__padata_remove_cpu(which calls padata_alloc_pd) it appears that
padata cpumask and
cpu_active_mask aren't intersect. Hence the following code in
padata_alloc_pd causes
a DZ error exception:
cpumask_and(pd->cpumask, cpumask, cpu_active_mask); // pd->cpumask
will be empty
...
num_cpus = cpumask_weight(pd->cpumask); // num_cpus = 0
pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1; // DZ!


Signed-off-by: Dan Kruchinin <dkruchinin@acm.org>
---
kernel/padata.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index fdd8ae6..dbe6d26 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -434,7 +434,7 @@ static struct parallel_data
*padata_alloc_pd(struct padata_instance *pinst,
atomic_set(&queue->num_obj, 0);
}

- num_cpus = cpumask_weight(pd->cpumask);
+ num_cpus = cpumask_weight(pd->cpumask) + 1;
pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1;

setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd);
--
1.7.1

--
W.B.R.
Dan Kruchinin


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