linux-kernel - [PATCH 04/11] RAS/CEC: Check count

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Date:   Thu,  9 May 2019 20:09:19 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tony Luck <tony.luck@...el.com>
Cc:     linux-edac <linux-edac@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 04/11] RAS/CEC: Check count_threshold unconditionally

From: Borislav Petkov <bp@...e.de>

The count_threshold should be checked unconditionally, after insertion
too, so that a count_threshold value of 1 can cause an immediate
offlining. I.e., offline the page on the *first* error encountered.

Add comments to make it clear what cec_add_elem() does, while at it.

Reported-by: WANG Chao <chao.wang@...oud.cn>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: linux-edac@...r.kernel.org
Link: https://lkml.kernel.org/r/20190418034115.75954-3-chao.wang@ucloud.cn
---
 drivers/ras/cec.c | 27 ++++++++++-----------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
index 1275907ff21c..73216b7f67be 100644
--- a/drivers/ras/cec.c
+++ b/drivers/ras/cec.c
@@ -294,6 +294,7 @@ int cec_add_elem(u64 pfn)
 
 	ca->ces_entered++;
 
+	/* Array full, free the LRU slot. */
 	if (ca->n == MAX_ELEMS)
 		WARN_ON(!del_lru_elem_unlocked(ca));
 
@@ -306,24 +307,17 @@ int cec_add_elem(u64 pfn)
 			(void *)&ca->array[to],
 			(ca->n - to) * sizeof(u64));
 
-		ca->array[to] = (pfn << PAGE_SHIFT) |
-				(DECAY_MASK << COUNT_BITS) | 1;
-
+		ca->array[to] = pfn << PAGE_SHIFT;
 		ca->n++;
-
-		ret = 0;
-
-		goto decay;
 	}
 
-	count = COUNT(ca->array[to]);
-
-	if (count < count_threshold) {
-		ca->array[to] |= (DECAY_MASK << COUNT_BITS);
-		ca->array[to]++;
+	/* Add/refresh element generation and increment count */
+	ca->array[to] |= DECAY_MASK << COUNT_BITS;
+	ca->array[to]++;
 
-		ret = 0;
-	} else {
+	/* Check action threshold and soft-offline, if reached. */
+	count = COUNT(ca->array[to]);
+	if (count >= count_threshold) {
 		u64 pfn = ca->array[to] >> PAGE_SHIFT;
 
 		if (!pfn_valid(pfn)) {
@@ -338,15 +332,14 @@ int cec_add_elem(u64 pfn)
 		del_elem(ca, to);
 
 		/*
-		 * Return a >0 value to denote that we've reached the offlining
-		 * threshold.
+		 * Return a >0 value to callers, to denote that we've reached
+		 * the offlining threshold.
 		 */
 		ret = 1;
 
 		goto unlock;
 	}
 
-decay:
 	ca->decay_count++;
 
 	if (ca->decay_count >= CLEAN_ELEMS)
-- 
2.21.0