Hi Clemens and Iwai-san,
I found a critical bug on ALSA IEC 61883-1/6 engine at error handling on process context. At packet queueing error or detection of invalid packet, user process can stall on local CPU with IRQ disabled. This bug was introduced at v3.5.
I wrote a fix but this can be applied down to v4.9.31, but it's unavailable for the former longterm versions. What can we do for them?
========== 8< ---------- From c8c7541f83913c98bb6f3774127a48c7998caca0 Mon Sep 17 00:00:00 2001 From: Takashi Sakamoto o-takashi@sakamocchi.jp Date: Fri, 9 Jun 2017 07:40:05 +0900 Subject: [PATCH] ALSA: firewire-lib: Fix stall of process context on local CPU with disabled IRQ at packet error
At Linux v3.5, packet processing can be done in process context of ALSA PCM application as well as software IRQ context for OHCI 1394. Below is an example of the callgraph (some calls are omitted).
ioctl(2) with e.g. HWSYNC (sound/core/pcm_native.c) ->snd_pcm_common_ioctl1() ->snd_pcm_hwsync() ->snd_pcm_stream_lock_irq (sound/core/pcm_lib.c) ->snd_pcm_update_hw_ptr() ->snd_pcm_udpate_hw_ptr0() ->struct snd_pcm_ops.pointer() (sound/firewire/*) = Each handler on drivers in ALSA firewire stack (sound/firewire/amdtp-stream.c) ->amdtp_stream_pcm_pointer() (drivers/firewire/core-iso.c) ->fw_iso_context_flush_completions() ->struct fw_card_driver.flush_iso_completion() (drivers/firewire/ohci.c) = flush_iso_completions() ->struct fw_iso_context.callback.sc (sound/firewire/amdtp-stream.c) = in_stream_callback() or out_stream_callback() ->... ->snd_pcm_stream_unlock_irq
When packet queueing error occurs or detecting invalid packets in 'in_stream_callback()' or 'out_stream_callback()', 'snd_pcm_stop_xrun()' is called on local CPU with disabled IRQ.
(sound/firewire/amdtp-stream.c) in_stream_callback() or out_stream_callback() ->amdtp_stream_pcm_abort() ->snd_pcm_stop_xrun() ->snd_pcm_stream_lock_irqsave() ->snd_pcm_stop() ->snd_pcm_stream_unlock_irqrestore()
The process is stalled on the CPU.
[ 562.630853] INFO: rcu_sched detected stalls on CPUs/tasks: [ 562.630861] 2-...: (1 GPs behind) idle=37d/140000000000000/0 softirq=38323/38323 fqs=7140 [ 562.630862] (detected by 3, t=15002 jiffies, g=21036, c=21035, q=5933) [ 562.630866] Task dump for CPU 2: [ 562.630867] alsa-source-OXF R running task 0 6619 1 0x00000008 [ 562.630870] Call Trace: [ 562.630876] ? vt_console_print+0x79/0x3e0 [ 562.630880] ? msg_print_text+0x9d/0x100 [ 562.630883] ? up+0x32/0x50 [ 562.630885] ? irq_work_queue+0x8d/0xa0 [ 562.630886] ? console_unlock+0x2b6/0x4b0 [ 562.630888] ? vprintk_emit+0x312/0x4a0 [ 562.630892] ? dev_vprintk_emit+0xbf/0x230 [ 562.630895] ? do_sys_poll+0x37a/0x550 [ 562.630897] ? dev_printk_emit+0x4e/0x70 [ 562.630900] ? __dev_printk+0x3c/0x80 [ 562.630903] ? _raw_spin_lock+0x20/0x30 [ 562.630909] ? snd_pcm_stream_lock+0x31/0x50 [snd_pcm] [ 562.630914] ? _snd_pcm_stream_lock_irqsave+0x2e/0x40 [snd_pcm] [ 562.630918] ? snd_pcm_stop_xrun+0x16/0x70 [snd_pcm] [ 562.630922] ? in_stream_callback+0x3e6/0x450 [snd_firewire_lib] [ 562.630925] ? handle_ir_packet_per_buffer+0x8e/0x1a0 [firewire_ohci] [ 562.630928] ? ohci_flush_iso_completions+0xa3/0x130 [firewire_ohci] [ 562.630932] ? fw_iso_context_flush_completions+0x15/0x20 [firewire_core] [ 562.630935] ? amdtp_stream_pcm_pointer+0x2d/0x40 [snd_firewire_lib] [ 562.630938] ? pcm_capture_pointer+0x19/0x20 [snd_oxfw] [ 562.630943] ? snd_pcm_update_hw_ptr0+0x47/0x3d0 [snd_pcm] [ 562.630945] ? poll_select_copy_remaining+0x150/0x150 [ 562.630947] ? poll_select_copy_remaining+0x150/0x150 [ 562.630952] ? snd_pcm_update_hw_ptr+0x10/0x20 [snd_pcm] [ 562.630956] ? snd_pcm_hwsync+0x45/0xb0 [snd_pcm] [ 562.630960] ? snd_pcm_common_ioctl1+0x1ff/0xc90 [snd_pcm] [ 562.630962] ? futex_wake+0x90/0x170 [ 562.630966] ? snd_pcm_capture_ioctl1+0x136/0x260 [snd_pcm] [ 562.630970] ? snd_pcm_capture_ioctl+0x27/0x40 [snd_pcm] [ 562.630972] ? do_vfs_ioctl+0xa3/0x610 [ 562.630974] ? vfs_read+0x11b/0x130 [ 562.630976] ? SyS_ioctl+0x79/0x90 [ 562.630978] ? entry_SYSCALL_64_fastpath+0x1e/0xad
This commit attempts to fix the above bug by removing the calls of 'amdtp_stream_pcm_abort()' from packet handler. When encountering the error state, the packet handler is already programmed not to process packets anymore. This commit expects any process context or software IRQ contexts to detect PCM XRUN by calls of snd_pcm_hw_ptr() or checking status data of PCM substream.
Fixes: e9148dddc3c7("ALSA: firewire-lib: flush completed packets when reading PCM position") Signed-off-by: Takashi Sakamoto o-takashi@sakamocchi.jp --- sound/firewire/amdtp-stream.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c index 4316d9db404d..65e215764c21 100644 --- a/sound/firewire/amdtp-stream.c +++ b/sound/firewire/amdtp-stream.c @@ -682,7 +682,6 @@ static void out_stream_callback(struct fw_iso_context *context, u32 tstamp, cycle = increment_cycle_count(cycle, 1); if (s->handle_packet(s, 0, cycle, i) < 0) { s->packet_index = -1; - amdtp_stream_pcm_abort(s); return; } } @@ -734,7 +733,6 @@ static void in_stream_callback(struct fw_iso_context *context, u32 tstamp, /* Queueing error or detecting invalid payload. */ if (i < packets) { s->packet_index = -1; - amdtp_stream_pcm_abort(s); return; }