Re: [PATCH v2 07/10] perf/hisi_pcie: Avoid placing cpumask var on stack

[Jonathan Cameron]

On Wed, 3 Apr 2024 15:35:10 +0100
Mark Rutland <mark.rutland@xxxxxxx> wrote:

> On Wed, Apr 03, 2024 at 08:51:06PM +0800, Dawei Li wrote:
> > For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask
> > variable on stack is not recommended since it can cause potential stack
> > overflow.
> > 
> > Instead, kernel code should always use *cpumask_var API(s) to allocate
> > cpumask var in config-neutral way, leaving allocation strategy to
> > CONFIG_CPUMASK_OFFSTACK.
> > 
> > But dynamic allocation in cpuhp's teardown callback is somewhat problematic
> > for if allocation fails(which is unlikely but still possible):
> > - If -ENOMEM is returned to caller, kernel crashes for non-bringup
> >   teardown;
> > - If callback pretends nothing happened and returns 0 to caller, it may
> >   trap system into an in-consisitent/compromised state;
> > 
> > Use newly-introduced cpumask_any_and_but() to address all issues above.
> > It eliminates usage of temporary cpumask var in generic way, no matter how
> > the cpumask var is allocated.
> > 
> > Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
> > Signed-off-by: Dawei Li <dawei.li@xxxxxxxxxxxx>  
> 
> The logic looks good to me, but I'd like the commit message updated the same as
> per my comment on patch 2.
> 
> With that commit message:
> 
> Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>

Acked-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

> 
> Mark.
> 
> > ---
> >  drivers/perf/hisilicon/hisi_pcie_pmu.c | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/perf/hisilicon/hisi_pcie_pmu.c b/drivers/perf/hisilicon/hisi_pcie_pmu.c
> > index 5d1f0e9fdb08..06b192cc31d5 100644
> > --- a/drivers/perf/hisilicon/hisi_pcie_pmu.c
> > +++ b/drivers/perf/hisilicon/hisi_pcie_pmu.c
> > @@ -673,7 +673,6 @@ static int hisi_pcie_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
> >  {
> >  	struct hisi_pcie_pmu *pcie_pmu = hlist_entry_safe(node, struct hisi_pcie_pmu, node);
> >  	unsigned int target;
> > -	cpumask_t mask;
> >  	int numa_node;
> >  
> >  	/* Nothing to do if this CPU doesn't own the PMU */
> > @@ -684,10 +683,10 @@ static int hisi_pcie_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
> >  
> >  	/* Choose a local CPU from all online cpus. */
> >  	numa_node = dev_to_node(&pcie_pmu->pdev->dev);
> > -	if (cpumask_and(&mask, cpumask_of_node(numa_node), cpu_online_mask) &&
> > -	    cpumask_andnot(&mask, &mask, cpumask_of(cpu)))
> > -		target = cpumask_any(&mask);
> > -	else
> > +
> > +	target = cpumask_any_and_but(cpumask_of_node(numa_node),
> > +				     cpu_online_mask, cpu);
> > +	if (target >= nr_cpu_ids)
> >  		target = cpumask_any_but(cpu_online_mask, cpu);
> >  
> >  	if (target >= nr_cpu_ids) {
> > -- 
> > 2.27.0
> >