From 174f0582e38abe03b88e15f04bfe58490f88cb19 Mon Sep 17 00:00:00 2001 From: Zide Chen Date: Thu, 11 Jun 2026 09:00:32 -0700 Subject: [PATCH] perf/x86/intel/uncore: Fix uncore_box ref/unref ordering 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: c74443d92f68 ("perf/x86/uncore: Support per PMU cpumask") Signed-off-by: Zide Chen Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ian Rogers Reviewed-by: Dapeng Mi Link: https://patch.msgid.link/20260611160033.66760-8-zide.chen@intel.com --- arch/x86/events/intel/uncore.c | 50 ++++++++++++++++------------------ 1 file changed, 23 insertions(+), 27 deletions(-) diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c index feb8c3b0076b..b9ac2f7d31ca 100644 --- a/arch/x86/events/intel/uncore.c +++ b/arch/x86/events/intel/uncore.c @@ -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; }