2.6.38+ hard lockup in pcm_lib.c

I had a consistent hard-lockup on one of my machines, an Amd X6, just after Kdm loaded the desktop (most certainly when it decides to start talking to the sound card). Everything was dead, even ssh access to the computer. I git bisected it until I found the commit that was causing it. After reverting the patch everything is fine. This is the only one of four computers that had the problem. Here's the revert patch (so I can get some expert eyeballs looking at what may be the problem).

@@ -375,22 +375,6 @@ static int snd_pcm_update_hw_ptr0(struct
      }
 
      if (runtime->no_period_wakeup) {
-        /*
-         * Without regular period interrupts, we have to check
-         * the elapsed time to detect xruns.
-         */
-        jdelta = jiffies - runtime->hw_ptr_jiffies;
-        if (jdelta < runtime->hw_ptr_buffer_jiffies / 2)
-            goto no_delta_check;
-        hdelta = jdelta - delta * HZ / runtime->rate;
-        while (hdelta > runtime->hw_ptr_buffer_jiffies / 2 + 1) {
-            delta += runtime->buffer_size;
-            hw_base += runtime->buffer_size;
-            if (hw_base >= runtime->boundary)
-                hw_base = 0;
-            new_hw_ptr = hw_base + pos;
-            hdelta -= runtime->hw_ptr_buffer_jiffies;
-        }
          goto no_delta_check;
      }
 

59ff878ffb26bc0be812ca8295799164f413ae88 is the first bad commit commit 59ff878ffb26bc0be812ca8295799164f413ae88

Author: Clemens Ladisch
Date:   Thu Nov 18 09:43:52 2010 +0100

ALSA: pcm: detect xruns in no-period-wakeup mode

When period wakeups are disabled, successive calls to the pointer
update
function do not have a maximum allowed distance, so xruns cannot be detected with the pointer value only.

To detect xruns, compare the actually elapsed time with the time that should have theoretically elapsed since the last update. When the hardware pointer has wrapped around due to an xrun, the actually
elapsed
time will be too big by about hw_ptr_buffer_jiffies.

:040000 040000 5daac6baa3aaecbe4a030955a1cfe9714178019a
94f07701413dff5712c8fa5e60d93ef909864cc0 M sound

This looks as if you get an infinite loop, probably because hw_ptr_buffer_jiffies is zero.

Please try this patch:

@@ -425,6 +425,8 @@ static int snd_pcm_hw_params(struct snd_
 	runtime->no_period_wakeup =
 			(params->info & SNDRV_PCM_INFO_NO_PERIOD_WAKEUP) &&
 			(params->flags & SNDRV_PCM_HW_PARAMS_NO_PERIOD_WAKEUP);
+	runtime->hw_ptr_buffer_jiffies =
+			max(1uL, (runtime->buffer_size * HZ) / runtime->rate);
 
 	bits = snd_pcm_format_physical_width(runtime->format);
 	runtime->sample_bits = bits;

@@ -866,8 +868,6 @@ static void snd_pcm_post_start(struct sn
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	snd_pcm_trigger_tstamp(substream);
 	runtime->hw_ptr_jiffies = jiffies;
-	runtime->hw_ptr_buffer_jiffies = (runtime->buffer_size * HZ) / 
-							    runtime->rate;
 	runtime->status->state = state;
 	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
 	    runtime->silence_size > 0)