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

[Kelly Anderson]

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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