linux-kernel - Re: Linux 2.6.38 freeze because of sound/core/pcm_lib.c commit 59ff878ffb26bc0be812ca8295799164f413ae88

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Message-ID: <4D952B76.7000201@silka.with-linux.com>
Date:	Thu, 31 Mar 2011 19:33:42 -0600
From:	Kelly Anderson <kelly@...ka.with-linux.com>
To:	"Christopher K." <c.krooss@...glemail.com>
CC:	Clemens Ladisch <clemens@...isch.de>, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org
Subject: Re: Linux 2.6.38 freeze because of sound/core/pcm_lib.c commit 59ff878ffb26bc0be812ca8295799164f413ae88

On 03/31/11 15:50, Kelly Anderson wrote:
>
> Just to let you know.  I'm using a gtx460 also.  I haven't had a 
> chance to reboot into the newly patched kernel yet.  It is interesting 
> that we both have gtx460's.  I have a machine with a gtx430 that 
> doesn't seem to exhibit the problem.
>
> cat /etc/modprobe.d/snd_hda_intel.conf
>
> options snd-hda-intel probe_mask=-1,0xa
>
OK, I debugged the problem and came up with a solution.  The bottom line 
is that it's a problem with a signed to unsigned compare.  First the fix:

--- ./sound/core/pcm_lib.c.orig    2011-03-27 12:37:20.000000000 -0600
+++ ./sound/core/pcm_lib.c    2011-03-31 19:01:35.392739127 -0600
@@ -379,17 +379,17 @@ static int snd_pcm_update_hw_ptr0(struct
           * 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)
+        jdelta = (snd_pcm_sframes_t)(jiffies - runtime->hw_ptr_jiffies);
+        if (jdelta < (snd_pcm_sframes_t)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) {
+        while (hdelta > 
(snd_pcm_sframes_t)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;
+            hdelta -= (snd_pcm_sframes_t)runtime->hw_ptr_buffer_jiffies;
          }
          goto no_delta_check;
      }

And here's the patch I used to debug the problem:

--- ./sound/core/pcm_lib.c.orig    2011-03-27 12:37:20.000000000 -0600
+++ ./sound/core/pcm_lib.c    2011-03-31 18:44:23.701411841 -0600
@@ -379,18 +379,31 @@ static int snd_pcm_update_hw_ptr0(struct
           * Without regular period interrupts, we have to check
           * the elapsed time to detect xruns.
           */
+        int loopCount = 0;
+        BUG_ON(runtime->hw_ptr_jiffies < 0);
+        BUG_ON(runtime->hw_ptr_jiffies == 0);
+        BUG_ON(runtime->hw_ptr_jiffies > jiffies);
          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) {
+        printk(KERN_INFO "Before loop: jdelta=%ld, hdelta=%ld 
runtime->hw_ptr_buffer_jiffies=%lu\n"
+                        , jdelta , hdelta , 
runtime->hw_ptr_buffer_jiffies);
+        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;
+            hdelta -= runtime->hw_ptr_buffer_jiffies;
+            if (++loopCount >= 1024*1024*4)
+            {
+                printk(KERN_INFO "stopped the madness at 4 thousand\n");
+                break;
+            }
          }
+        printk(KERN_INFO "After loop: jdelta=%ld, hdelta=%ld 
runtime->hw_ptr_buffer_jiffies=%lu\n"
+                        , jdelta , hdelta , 
runtime->hw_ptr_buffer_jiffies);
          goto no_delta_check;
      }


The kernel output with the testing patch applied:

Mar 31 18:37:02 speedy kernel: Before loop: jdelta=352, hdelta=352 
runtime->hw_ptr_buffer_jiffies=371
Mar 31 18:37:02 speedy kernel: stopped the madness at 4 million
Mar 31 18:37:02 speedy kernel: After loop: jdelta=352, 
hdelta=-1556086432 runtime->hw_ptr_buffer_jiffies=371


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