On 08/07/2014 04:48 AM, Ralf Baechle wrote:
On Tue, Aug 05, 2014 at 01:37:47PM +0800, Wei.Yang@xxxxxxxxxxxxx wrote:
From: Yang Wei <Wei.Yang@xxxxxxxxxxxxx>
In RT kernel, I ran into the following calltrace, so PMU interrupts cannot
be threaded
in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
INFO: lockdep is turned off.
Call Trace:
[<ffffffff8088595c>] dump_stack+0x1c/0x50
[<ffffffff801a958c>] __might_sleep+0x13c/0x148
[<ffffffff80891c54>] rt_spin_lock+0x3c/0xb0
[<ffffffff801ad29c>] __wake_up+0x3c/0x80
[<ffffffff80243ba4>] perf_event_wakeup+0x8c/0xf8
[<ffffffff80243c50>] perf_pending_event+0x40/0x78
[<ffffffff8023d88c>] irq_work_run+0x74/0xc0
[<ffffffff80152640>] mipsxx_pmu_handle_shared_irq+0x110/0x228
[<ffffffff8015276c>] mipsxx_pmu_handle_irq+0x14/0x30
[<ffffffff801ffda4>] handle_irq_event_percpu+0xbc/0x470
[<ffffffff80204478>] handle_percpu_irq+0x98/0xc8
[<ffffffff801ff284>] generic_handle_irq+0x4c/0x68
[<ffffffff8089748c>] do_IRQ+0x2c/0x48
[<ffffffff80105864>] plat_irq_dispatch+0x64/0xd0
Hm... I don't see why based on this backtrace you concluce the
handler needs to be marked IRQF_NO_THREAD. However there's another
reason to mark it IRQF_NO_THREAD. IRQ threads may be rescheduled to
other CPUs but this handler is fiddling with per-CPU resources.
Also by its nature, the profiling code needs synchronous access to the
register state of the interrupted code. If you are running on a
different thread, then I don't think this would be available.
See https://patchwork.linux-mips.org/patch/2818/ for a similar
scenario a few years ago.
Ralf
