[PATCH 2/6] driver edac mod race fix i82875p

[dougthompson@xmission.com]

From:	Jason Uhlenkott <juhlenko@akamai.com>

If ERRSTS indicates that there's no error then we don't need to bother
reading the other registers.

In addition to making the common case faster, this actually fixes a
small race where we don't see an error but we clear the error bits
anyway, potentially wiping away info on an error that happened in the
interim (or where a CE arrives between the first and second read of
ERRSTS, causing us to falsely claim "UE overwrote CE").

Signed-off-by:	Jason Uhlenkott <juhlenko@akamai.com>
Signed-off-by:	Douglas Thompson <dougthompson@xmission.com>
Cc:	alan@lxorguk.ukuu.org.uk
---
 i82875p_edac.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- linux.orig/drivers/edac/i82875p_edac.c	2007-05-21 00:46:31.568356390 -0400
+++ linux/drivers/edac/i82875p_edac.c	2007-05-21 00:46:36.637650484 -0400
@@ -198,27 +198,28 @@
 	 * overwritten by UE.
 	 */
 	pci_read_config_word(pdev, I82875P_ERRSTS, &info->errsts);
+
+	if (!(info->errsts & 0x0081))
+		return;
+
 	pci_read_config_dword(pdev, I82875P_EAP, &info->eap);
 	pci_read_config_byte(pdev, I82875P_DES, &info->des);
 	pci_read_config_byte(pdev, I82875P_DERRSYN, &info->derrsyn);
 	pci_read_config_word(pdev, I82875P_ERRSTS, &info->errsts2);
 
-	pci_write_bits16(pdev, I82875P_ERRSTS, 0x0081, 0x0081);
-
 	/*
 	 * If the error is the same then we can for both reads then
 	 * the first set of reads is valid.  If there is a change then
 	 * there is a CE no info and the second set of reads is valid
 	 * and should be UE info.
 	 */
-	if (!(info->errsts2 & 0x0081))
-		return;
-
 	if ((info->errsts ^ info->errsts2) & 0x0081) {
 		pci_read_config_dword(pdev, I82875P_EAP, &info->eap);
 		pci_read_config_byte(pdev, I82875P_DES, &info->des);
 		pci_read_config_byte(pdev, I82875P_DERRSYN, &info->derrsyn);
 	}
+
+	pci_write_bits16(pdev, I82875P_ERRSTS, 0x0081, 0x0081);
 }
 
 static int i82875p_process_error_info(struct mem_ctl_info *mci,
@@ -229,7 +230,7 @@
 
 	multi_chan = mci->csrows[0].nr_channels - 1;
 
-	if (!(info->errsts2 & 0x0081))
+	if (!(info->errsts & 0x0081))
 		return 0;
 
 	if (!handle_errors)

-
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