Messages in this thread | | | Date | Wed, 16 Mar 2022 14:50:11 -0700 | Subject | Re: [PATCH v3 07/21] x86/resctrl: Create mba_sc configuration in the rdt_domain | From | Reinette Chatre <> |
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Hi James,
I tried out this work and encountered a null pointer de-reference that seems related to this patch. After digging into that it is not clear to me how this is expected to work.
I encounter the issue just by attempting to mount with "-o mba_MBps" which is the way to enable the mba_sc and exactly what this patch aims to address.
More below ...
On 2/17/2022 10:20 AM, James Morse wrote: > To support resctrl's MBA software controller, the architecture must provide > a second configuration array to hold the mbps_val[] from user-space. > > This complicates the interface between the architecture specific code and > the filesystem portions of resctrl that will move to /fs/, to allow > multiple architectures to support resctrl. > > Make the filesystem parts of resctrl create an array for the mba_sc > values when is_mba_sc() is set to true. The software controller > can be changed to use this, allowing the architecture code to only > consider the values configured in hardware. > > Signed-off-by: James Morse <james.morse@arm.com> > ---
...
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > index 794a84ba9097..e4313f907eb6 100644 > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > @@ -1889,6 +1889,30 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r) > l3_qos_cfg_update(&hw_res->cdp_enabled); > } > > +static int mba_sc_domain_allocate(struct rdt_resource *r, struct rdt_domain *d) > +{ > + u32 num_closid = resctrl_arch_get_num_closid(r); > + int cpu = cpumask_any(&d->cpu_mask); > + int i; > + > + d->mbps_val = kcalloc_node(num_closid, sizeof(*d->mbps_val), > + GFP_KERNEL, cpu_to_node(cpu)); > + if (!d->mbps_val) > + return -ENOMEM; > + > + for (i = 0; i < num_closid; i++) > + d->mbps_val[i] = MBA_MAX_MBPS; > + > + return 0; > +} > +
...
> @@ -1905,6 +1932,11 @@ static int set_mba_sc(bool mba_sc) > > r->membw.mba_sc = mba_sc; > > + list_for_each_entry(d, &r->domains, list) { > + for (i = 0; i < num_closid; i++) > + d->mbps_val[i] = MBA_MAX_MBPS; > + } > + > return 0; > } >
...
> @@ -3309,6 +3344,12 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d) > if (err) > return err; > > + err = mba_sc_domain_allocate(r, d); > + if (err) { > + domain_destroy_mon_state(d); > + return err; > + } > +
Before the above snippet there is a check if the resource is capable of monitoring:
resctrl_online_domain() { ... if (!r->mon_capable) return 0;
... err = mba_sc_domain_allocate(r, d); ... }
Thus, the rdt_domain->mbps_val array will only exist in those resources that support monitoring. Taking a look at where mon_capable is set we see it is done in get_rdt_mon_resources() and as you can see it is only done for RDT_RESOURCE_L3.
get_rdt_mon_resources() { struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
...
return !rdt_get_mon_l3_config(r); /* mon_capable is set within */ }
Based on the above the rdt_domain->mbps_val array can only exist for those domains that belong to resource RDT_RESOURCE_L3 (if it is capable of monitoring).
Now, looking at set_mba_sc() changed here, it only interacts with RDT_RESOURCE_MBA:
set_mba_sc() { struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
...
list_for_each_entry(d, &r->domains, list) { for (i = 0; i < num_closid; i++) d->mbps_val[i] = MBA_MAX_MBPS; } } Considering that no domain belonging to RDT_RESOURCE_MBA will have this array this always ends up being a null pointer de-reference.
Reinette
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