EDAC, i7core: Remove double buffering of error records

In the bad old days the functions from x86_mce_decoder_chain could be
called in machine check context. So we used to carefully copy them and
defer processing until later. But in

  f29a7af ("x86/mce: Avoid potential deadlock due to printk() in MCE context")

we switched the logging code to save the record in a genpool, and call
the functions that registered to be notified later from a work queue.

So drop all the double buffering and do all the work we want to do as
soon as i7core_mce_check_error() is called.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/29ab2c370915c6e132fc5d88e7b72cb834bedbfe.1461855008.git.tony.luck@intel.com
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/i7core_edac.c

@@ -271,16 +271,6 @@ struct i7core_pvt {
 
 	bool		is_registered, enable_scrub;
 
-	/* Fifo double buffers */
-	struct mce		mce_entry[MCE_LOG_LEN];
-	struct mce		mce_outentry[MCE_LOG_LEN];
-
-	/* Fifo in/out counters */
-	unsigned		mce_in, mce_out;
-
-	/* Count indicator to show errors not got */
-	unsigned		mce_overrun;
-
 	/* DCLK Frequency used for computing scrub rate */
 	int			dclk_freq;
 
@@ -1792,69 +1782,24 @@ static void i7core_mce_output_error(struct mem_ctl_info *mci,
  *	i7core_check_error	Retrieve and process errors reported by the
  *				hardware. Called by the Core module.
  */
-static void i7core_check_error(struct mem_ctl_info *mci)
+static void i7core_check_error(struct mem_ctl_info *mci, struct mce *m)
 {
 	struct i7core_pvt *pvt = mci->pvt_info;
-	int i;
-	unsigned count = 0;
-	struct mce *m;
 
-	/*
-	 * MCE first step: Copy all mce errors into a temporary buffer
-	 * We use a double buffering here, to reduce the risk of
-	 * losing an error.
-	 */
-	smp_rmb();
-	count = (pvt->mce_out + MCE_LOG_LEN - pvt->mce_in)
-		% MCE_LOG_LEN;
-	if (!count)
-		goto check_ce_error;
-
-	m = pvt->mce_outentry;
-	if (pvt->mce_in + count > MCE_LOG_LEN) {
-		unsigned l = MCE_LOG_LEN - pvt->mce_in;
-
-		memcpy(m, &pvt->mce_entry[pvt->mce_in], sizeof(*m) * l);
-		smp_wmb();
-		pvt->mce_in = 0;
-		count -= l;
-		m += l;
-	}
-	memcpy(m, &pvt->mce_entry[pvt->mce_in], sizeof(*m) * count);
-	smp_wmb();
-	pvt->mce_in += count;
-
-	smp_rmb();
-	if (pvt->mce_overrun) {
-		i7core_printk(KERN_ERR, "Lost %d memory errors\n",
-			      pvt->mce_overrun);
-		smp_wmb();
-		pvt->mce_overrun = 0;
-	}
-
-	/*
-	 * MCE second step: parse errors and display
-	 */
-	for (i = 0; i < count; i++)
-		i7core_mce_output_error(mci, &pvt->mce_outentry[i]);
+	i7core_mce_output_error(mci, m);
 
 	/*
 	 * Now, let's increment CE error counts
 	 */
-check_ce_error:
 	if (!pvt->is_registered)
 		i7core_udimm_check_mc_ecc_err(mci);
 	else
 		i7core_rdimm_check_mc_ecc_err(mci);
 }
 
 /*
- * i7core_mce_check_error	Replicates mcelog routine to get errors
- *				This routine simply queues mcelog errors, and
- *				return. The error itself should be handled later
- *				by i7core_check_error.
- * WARNING: As this routine should be called at NMI time, extra care should
- * be taken to avoid deadlocks, and to be as fast as possible.
+ * Check that logging is enabled and that this is the right type
+ * of error for us to handle.
  */
 static int i7core_mce_check_error(struct notifier_block *nb, unsigned long val,
 				  void *data)
@@ -1882,21 +1827,7 @@ static int i7core_mce_check_error(struct notifier_block *nb, unsigned long val,
 	if (mce->bank != 8)
 		return NOTIFY_DONE;
 
-	smp_rmb();
-	if ((pvt->mce_out + 1) % MCE_LOG_LEN == pvt->mce_in) {
-		smp_wmb();
-		pvt->mce_overrun++;
-		return NOTIFY_DONE;
-	}
-
-	/* Copy memory error at the ringbuffer */
-	memcpy(&pvt->mce_entry[pvt->mce_out], mce, sizeof(*mce));
-	smp_wmb();
-	pvt->mce_out = (pvt->mce_out + 1) % MCE_LOG_LEN;
-
-	/* Handle fatal errors immediately */
-	if (mce->mcgstatus & 1)
-		i7core_check_error(mci);
+	i7core_check_error(mci, mce);
 
 	/* Advise mcelog that the errors were handled */
 	return NOTIFY_STOP;
@@ -2243,8 +2174,6 @@ static int i7core_register_mci(struct i7core_dev *i7core_dev)
 	get_dimm_config(mci);
 	/* record ptr to the generic device */
 	mci->pdev = &i7core_dev->pdev[0]->dev;
-	/* Set the function pointer to an actual operation function */
-	mci->edac_check = i7core_check_error;
 
 	/* Enable scrubrate setting */
 	if (pvt->enable_scrub)