MIPS: perf: fix deadlock

mipsxx_pmu_handle_shared_irq() calls irq_work_run() while holding the
pmuint_rwlock for read. irq_work_run() can, via perf_pending_event(),
call try_to_wake_up() which can try to take rq->lock.

However, perf can also call perf_pmu_enable() (and thus take the
pmuint_rwlock for write) while holding the rq->lock, from
finish_task_switch() via perf_event_context_sched_in().

This leads to an ABBA deadlock:

PID: 3855 TASK: 8f7ce288 CPU: 2 COMMAND: "process"
#0 [89c39ac8] __delay at 803b5be4
#1 [89c39ac8] do_raw_spin_lock at 8008fdcc
#2 [89c39af8] try_to_wake_up at 8006e47c
#3 [89c39b38] pollwake at 8018eab0
#4 [89c39b68] __wake_up_common at 800879f4
#5 [89c39b98] __wake_up at 800880e4
#6 [89c39bc8] perf_event_wakeup at 8012109c
#7 [89c39be8] perf_pending_event at 80121184
#8 [89c39c08] irq_work_run_list at 801151f0
#9 [89c39c38] irq_work_run at 80115274
#10 [89c39c50] mipsxx_pmu_handle_shared_irq at 8002cc7c

PID: 1481 TASK: 8eaac6a8 CPU: 3 COMMAND: "process"
#0 [8de7f900] do_raw_write_lock at 800900e0
#1 [8de7f918] perf_event_context_sched_in at 80122310
#2 [8de7f938] __perf_event_task_sched_in at 80122608
#3 [8de7f958] finish_task_switch at 8006b8a4
#4 [8de7f998] __schedule at 805e4dc4
#5 [8de7f9f8] schedule at 805e5558
#6 [8de7fa10] schedule_hrtimeout_range_clock at 805e9984
#7 [8de7fa70] poll_schedule_timeout at 8018e8f8
#8 [8de7fa88] do_select at 8018f338
#9 [8de7fd88] core_sys_select at 8018f5cc
#10 [8de7fee0] sys_select at 8018f854
#11 [8de7ff28] syscall_common at 80028fc8

The lock seems to be there to protect the hardware counters so there is
no need to hold it across irq_work_run().

Signed-off-by: Rabin Vincent <[e-mail]>
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/kernel/perf_event_mipsxx.c

···
 	HANDLE_COUNTER(0)
 	}
 
+#ifdef CONFIG_MIPS_PERF_SHARED_TC_COUNTERS
+	read_unlock(&pmuint_rwlock);
+#endif
+	resume_local_counters();
+
 	/*
 	 * Do all the work for the pending perf events. We can do this
 	 * in here because the performance counter interrupt is a regular
···
 	if (handled == IRQ_HANDLED)
 		irq_work_run();
 
-#ifdef CONFIG_MIPS_PERF_SHARED_TC_COUNTERS
-	read_unlock(&pmuint_rwlock);
-#endif
-	resume_local_counters();
 	return handled;
 }