[BUG REPORT]: ARM64: perf: System hung in perf test

[Wangnan (F)]

System hung can be reproduced on qemu and real hardware using:

 # perf test -v signal

If qemu is started with '-smp 1', system hung. In real hardware and in
qemu with smp > 1, the result is:

 # /perf test -v signal
 17: Test breakpoint overflow signal handler                  :
 --- start ---
 test child forked, pid 792
 count1 11, count2 11, overflow 11
 failed: RF EFLAG recursion issue detected
 failed: wrong overflow hit
 failed: wrong count for bp2
 test child finished with -1
 ---- end ----
 Test breakpoint overflow signal handler: FAILED!

Looks like something like [1] is required for ARM64.

Some analysis is done with qemu:

This testcase tests the intertaction between breakpoint, perf_event
and signal handling. It installs a breakpoint at the enter of a
function and makes the corresponding perf_event generate SIGIO when
the event raise.

When perf_event on a async perf_event is triggered:

        if (*perf_event_fasync(event) && event->pending_kill) {
                event->pending_wakeup = 1;
                irq_work_queue(&event->pending);
        }

it calls irq_work_queue(&event->pending), which is used to fire a
poll event and SIGIO. Later when perf_event is closed, in _free_event
irq_work_sync(&event->pending) is called to ensure all irq_work is done.
On ARM64, if we have only 1 cpu, the system hung at irq_work_sync().

Using gdb attached, I see:
 1. IRQ is not disabled. Inside irq_work_sync, result of 
arch_local_save_flags()
    is 0x140.

 2. hrtimer_interrupt() is still generated. The system is not dead.

 3. In irq_work_tick, we have a chance to process irq_work. However,
    llist_empty(raised) is false but arch_irq_work_has_interrupt()
    is true, so kernel only process lazy_list.

 4. handle_IPI() is never called, so I guess the IPI is disabled by 
breakpoint
    and not restored in this case.

[1] 
http://lkml.kernel.org/r/1362940871-24486-1-git-send-email-jolsa@xxxxxxxxxx


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