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perf/x86/intel/uncore: Fix uncore_box ref/unref ordering

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In uncore_event_cpu_online(), uncore_box_ref() was called before
uncore_change_context().  uncore_box_ref() gates on box->cpu >= 0,
but box->cpu is still -1 at that point because uncore_change_context()
has not run yet.  As a result, the box is never initialized on the
first CPU to come online in a die, leaving it permanently
uninitialized in the single-CPU-per-die case.

Thus, box->refcnt is one count below the true value, and in the CPU
offline path, the box will be torn down on the second-to-last CPU.

In uncore_event_cpu_offline(), uncore_box_unref() was called after
uncore_change_context(), so box->cpu is already -1 when the collector
CPU goes offline, which prevents it from tearing down the box.

Fix by swapping the call order in both paths so that
uncore_box_{ref,unref}() runs at the point where box->cpu reflects
the correct context.

Move allocate_boxes() out of uncore_box_ref() to enable this
reordering.

Fixes: c74443d92f ("perf/x86/uncore: Support per PMU cpumask")
Signed-off-by: Zide Chen <zide.chen@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://patch.msgid.link/20260611160033.66760-8-zide.chen@intel.com
This commit is contained in:
Zide Chen 2026-06-11 09:00:32 -07:00 committed by Peter Zijlstra
parent 30c0a10956
commit 174f0582e3
1 changed files with 23 additions and 27 deletions
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50
arch/x86/events/intel/uncore.c
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@ -1580,9 +1580,15 @@ static int uncore_event_cpu_offline(unsigned int cpu)
{
int die, target;
/* Clear the references */
die = topology_logical_die_id(cpu);
uncore_box_unref(uncore_msr_uncores, die);
uncore_box_unref(uncore_mmio_uncores, die);
/* Check if exiting cpu is used for collecting uncore events */
if (!cpumask_test_and_clear_cpu(cpu, &uncore_cpu_mask))
goto unref;
return 0;
/* Find a new cpu to collect uncore events */
target = cpumask_any_but(topology_die_cpumask(cpu), cpu);
@ -1595,16 +1601,10 @@ static int uncore_event_cpu_offline(unsigned int cpu)
uncore_change_context(uncore_msr_uncores, cpu, target);
uncore_change_context(uncore_mmio_uncores, cpu, target);
uncore_change_context(uncore_pci_uncores, cpu, target);
unref:
/* Clear the references */
die = topology_logical_die_id(cpu);
uncore_box_unref(uncore_msr_uncores, die);
uncore_box_unref(uncore_mmio_uncores, die);
return 0;
}
static int allocate_boxes(struct intel_uncore_type **types,
static void allocate_boxes(struct intel_uncore_type **types,
unsigned int die, unsigned int cpu)
{
struct intel_uncore_box *box, *tmp;
@ -1621,8 +1621,10 @@ static int allocate_boxes(struct intel_uncore_type **types,
if (pmu->boxes[die] || uncore_pmu_broken(pmu))
continue;
box = uncore_alloc_box(type, cpu_to_node(cpu));
if (!box)
if (!box) {
uncore_pmu_set_broken(pmu);
goto cleanup;
}
box->pmu = pmu;
box->dieid = die;
list_add(&box->active_list, &allocated);
@ -1633,14 +1635,13 @@ static int allocate_boxes(struct intel_uncore_type **types,
list_del_init(&box->active_list);
box->pmu->boxes[die] = box;
}
return 0;
return;
cleanup:
list_for_each_entry_safe(box, tmp, &allocated, active_list) {
list_del_init(&box->active_list);
kfree(box);
}
return -ENOMEM;
}
static int uncore_box_ref(struct intel_uncore_type **types,
@ -1649,11 +1650,7 @@ static int uncore_box_ref(struct intel_uncore_type **types,
struct intel_uncore_type *type;
struct intel_uncore_pmu *pmu;
struct intel_uncore_box *box;
int i, ret;
ret = allocate_boxes(types, die, cpu);
if (ret)
return ret;
int i;
for (; *types; types++) {
type = *types;
@ -1669,27 +1666,26 @@ static int uncore_box_ref(struct intel_uncore_type **types,
static int uncore_event_cpu_online(unsigned int cpu)
{
int die, target, msr_ret, mmio_ret;
int die, target;
die = topology_logical_die_id(cpu);
msr_ret = uncore_box_ref(uncore_msr_uncores, die, cpu);
mmio_ret = uncore_box_ref(uncore_mmio_uncores, die, cpu);
allocate_boxes(uncore_msr_uncores, die, cpu);
allocate_boxes(uncore_mmio_uncores, die, cpu);
/*
* Check if there is an online cpu in the package
* which collects uncore events already.
*/
target = cpumask_any_and(&uncore_cpu_mask, topology_die_cpumask(cpu));
if (target < nr_cpu_ids)
return 0;
cpumask_set_cpu(cpu, &uncore_cpu_mask);
if (!msr_ret)
if (target >= nr_cpu_ids) {
cpumask_set_cpu(cpu, &uncore_cpu_mask);
uncore_change_context(uncore_msr_uncores, -1, cpu);
if (!mmio_ret)
uncore_change_context(uncore_mmio_uncores, -1, cpu);
uncore_change_context(uncore_pci_uncores, -1, cpu);
uncore_change_context(uncore_pci_uncores, -1, cpu);
}
uncore_box_ref(uncore_msr_uncores, die, cpu);
uncore_box_ref(uncore_mmio_uncores, die, cpu);
return 0;
}