mce, edac: Use an atomic notifier for MCEs decoding

Add an atomic notifier which ensures proper locking when conveying
MCE info to EDAC for decoding. The actual notifier call overrides a
default, negative priority notifier.

Note: make sure we register the default decoder only once since
mcheck_init() runs on each CPU.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <20091003065752.GA8935@liondog.tnic>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

drivers/edac/edac_mce_amd.c

@@ -3,7 +3,6 @@
 
 static bool report_gart_errors;
 static void (*nb_bus_decoder)(int node_id, struct err_regs *regs);
-static void (*orig_mce_callback)(struct mce *m);
 
 void amd_report_gart_errors(bool v)
 {
@@ -363,8 +362,10 @@ static inline void amd_decode_err_code(unsigned int ec)
 		pr_warning("Huh? Unknown MCE error 0x%x\n", ec);
 }
 
-static void amd_decode_mce(struct mce *m)
+static int amd_decode_mce(struct notifier_block *nb, unsigned long val,
+			   void *data)
 {
+	struct mce *m = (struct mce *)data;
 	struct err_regs regs;
 	int node, ecc;
 
@@ -420,20 +421,22 @@ static void amd_decode_mce(struct mce *m)
 	}
 
 	amd_decode_err_code(m->status & 0xffff);
+
+	return NOTIFY_STOP;
 }
 
+static struct notifier_block amd_mce_dec_nb = {
+	.notifier_call	= amd_decode_mce,
+};
+
 static int __init mce_amd_init(void)
 {
 	/*
 	 * We can decode MCEs for Opteron and later CPUs:
 	 */
 	if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
-	    (boot_cpu_data.x86 >= 0xf)) {
-		/* safe the default decode mce callback */
-		orig_mce_callback = x86_mce_decode_callback;
-
-		x86_mce_decode_callback = amd_decode_mce;
-	}
+	    (boot_cpu_data.x86 >= 0xf))
+		atomic_notifier_chain_register(&x86_mce_decoder_chain, &amd_mce_dec_nb);
 
 	return 0;
 }
@@ -442,7 +445,7 @@ early_initcall(mce_amd_init);
 #ifdef MODULE
 static void __exit mce_amd_exit(void)
 {
-	x86_mce_decode_callback = orig_mce_callback;
+	atomic_notifier_chain_unregister(&x86_mce_decoder_chain, &amd_mce_dec_nb);
 }
 
 MODULE_DESCRIPTION("AMD MCE decoder");