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

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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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arch/x86/events/intel/uncore.c

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