linux-kernel - [PATCH] sb_edac.c, kernel linux-3.2-rc6.

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Date:	Fri, 23 Dec 2011 16:35:21 -0500
From:	Karandeep Chahal <kchahal@....com>
To:	linux-kernel@...r.kernel.org
CC:	mchehab@...hat.com
Subject: [PATCH] sb_edac.c, kernel linux-3.2-rc6.

While testing Sandy Bridge EDAC module I discovered a problem in the way 
sb_edac was registering itself for machine check notifications. The 
symptoms of the problem include:
1. Injecting a machine check exception can cause the system to hang for 
10-15 seconds.
2. Removing and re-inserting the kernel module can cause panic.

The system hangs for 10-15 seconds because the sb_edac notifier gets 
called by the kernel (notifier_call_chain) 0xffffffff times ((u32)(-1)).

The problem occurs because sb_edac calls atomic_notifier_chain_register 
twice with the same static notifier_block structure. The function 
atomic_notifier_chain_register gets called once for each memory 
controller (MC) with the same structure. The patch, then, fixes this 
problem by making sure that sb_edac registers for machine check 
notifications only once.

Also copying Mauro Carvalho Chehab (maintainer of sb_edac) for the 
review of the patch.

Cheers,
Karan

--- linux-3.2-rc6/drivers/edac/sb_edac.c    2011-12-16 
21:36:26.000000000 -0500
+++ linux-3.2-rc6-new/drivers/edac/sb_edac.c    2011-12-23 
14:54:57.000000000 -0500
@@ -1661,9 +1661,6 @@
      debugf0("MC: " __FILE__ ": %s(): mci = %p, dev = %p\n",
          __func__, mci, &sbridge_dev->pdev[0]->dev);

-    atomic_notifier_chain_unregister(&x86_mce_decoder_chain,
- &sbridge_mce_dec);
-
      /* Remove MC sysfs nodes */
      edac_mc_del_mc(mci->dev);

@@ -1731,8 +1728,6 @@
          goto fail0;
      }

-    atomic_notifier_chain_register(&x86_mce_decoder_chain,
- &sbridge_mce_dec);
      return 0;

  fail0:
@@ -1861,8 +1856,11 @@

      pci_rc = pci_register_driver(&sbridge_driver);

-    if (pci_rc >= 0)
+    if (pci_rc >= 0) {
+         atomic_notifier_chain_register(&x86_mce_decoder_chain,
+ &sbridge_mce_dec);
          return 0;
+    }

      sbridge_printk(KERN_ERR, "Failed to register device with error %d.\n",
                pci_rc);
@@ -1877,6 +1875,9 @@
  static void __exit sbridge_exit(void)
  {
      debugf2("MC: " __FILE__ ": %s()\n", __func__);
+    atomic_notifier_chain_unregister(&x86_mce_decoder_chain,
+ &sbridge_mce_dec);
+
      pci_unregister_driver(&sbridge_driver);
  }

View attachment "me.patch" of type "text/x-patch" (1147 bytes)

View attachment "README" of type "text/plain" (187 bytes)