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3d8d741009
perf_pmu_sched_task() returns early when cpuctx->task_ctx is set and
leaves the work to perf_ctx_sched_task_cb(), which only walks
ctx->pmu_ctx_list. A PMU whose events are all CPU-wide is not on that
list, so nothing calls its sched_task(). With
perf record -b -e cycles -a -- ls
armv8pmu_sched_task() is skipped on every switch to a task that has a
perf context but no event on that PMU, and BRBE records leak across the
task boundary. intel_pmu_lbr_add() calls perf_sched_cb_inc()
unconditionally too, so LBR records leak the same way on x86.
Drop the early return and skip only the CPCs that
perf_ctx_sched_task_cb() handles. That one needs a gate of its own to
make the split exact: it tests cpc->sched_cb_usage, which
perf_sched_cb_inc() sets per CPU for every branch stack user, so a task
with an event for that PMU pinned to another CPU would be handled twice.
On x86 the second __intel_pmu_lbr_restore() finds lbr_stack_state ==
LBR_NONE and calls intel_pmu_lbr_reset(), throwing away the callstack
the first one restored.
cpc->task_epc is set only while a task context is scheduled in, and
there is one epc per PMU on ctx->pmu_ctx_list, so the two gates are
inverses.
For the CPCs perf_pmu_sched_task() picks up, the callback now runs
outside the perf_ctx_disable() and perf_ctx_enable() pair in
perf_event_context_sched_in(). __perf_pmu_sched_task() disables the PMU
around the call itself.
Fixes:
|
||
|---|---|---|
| .. | ||
| callchain.c | ||
| core.c | ||
| hw_breakpoint_test.c | ||
| hw_breakpoint.c | ||
| internal.h | ||
| Makefile | ||
| ring_buffer.c | ||
| uprobes.c | ||