Messages in this thread Patch in this message | | | Date | Fri, 2 Jul 2010 17:24:13 +0400 | Subject | Re: [PATCH] Fixed division by zero bug in kernel/padata.c | From | Dan Kruchinin <> |
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No problem. Here is fixed patch: -- 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. 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(and hence 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 | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/kernel/padata.c b/kernel/padata.c index fdd8ae6..dcddac0 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -435,6 +435,9 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst, }
num_cpus = cpumask_weight(pd->cpumask); + if (!num_cpus) + goto err_free_cpumask; + pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1;
setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd); @@ -446,6 +449,8 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
return pd;
+err_free_cpumask: + free_cpumask_var(pd->cpumask); err_free_queue: free_percpu(pd->queue); err_free_pd: -- 1.7.1
On Fri, Jul 2, 2010 at 4:56 PM, Steffen Klassert <steffen.klassert@secunet.com> wrote: > On Fri, Jul 02, 2010 at 03:59:54PM +0400, Dan Kruchinin wrote: >> 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! >> > > Good catch! > >> >> 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; >> > > num_cpus should stay the number of cpus in this cpumask, this is required > to handle a smooth overrun of the sequence numbers. > I think it's better to return with an error and to stop the instance > if somebody takes away the last cpu in our cpumask. We can't run with an > empty cpumask anyway. > > Let us look again at this on monday. > > Thanks again for catching this, > > Steffen >
-- W.B.R. Dan Kruchinin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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