[PATCH] hda-intel: Avoid divide by zero crash

["Jody@Tritech" <jody@nctritech.com>]

On my AMD780V chipset, hda_intel.c can crash the kernel with a divide by 
zero
for as-yet unknown reasons. A simple check for zero prevents it, though
the problem that causes it remains. Since the workaround is harmless and
won't affect anyone except victims of this bug, it should be safe; 
moreover,
because this crash can be triggered by a user-mode application, there are
denial of service implications on the systems affected by the bug without
the patch.
Signed-off-by: Jody Bruchon <jody@nctritech.com>
--- linux-2.6.33-rc6/sound/pci/hda/hda_intel.c  2010-01-29 
16:57:50.000000000 -0500
+++ linux-2.6.33-rc6-fix/sound/pci/hda/hda_intel.c      2010-02-06 
09:44:10.028348166 -0500
@@ -1878,6 +1878,12 @@

         if (!bdl_pos_adj[chip->dev_index])
                 return 1; /* no delayed ack */
+       if (azx_dev->period_bytes == 0) {
+               printk(KERN_WARNING
+                       "hda-intel: Divide by zero was avoided "
+                       "in azx_dev->period_bytes.\n");
+               return 0;
+       }
         if (pos % azx_dev->period_bytes > azx_dev->period_bytes / 2)
                 return 0; /* NG - it's below the period boundary */
         return 1; /* OK, it's fine */