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authorBorislav Petkov <bp@suse.de>2019-04-20 13:27:51 +0200
committerPaul Gortmaker <paul.gortmaker@windriver.com>2019-09-16 12:21:25 -0400
commitdd36baab4cfce946206049e86bed5a709f136eb5 (patch)
tree23088b1da106e7be08320f956015252c673953f1
parente6bb17d826a96f8d377b9db6100a1b2ffb4073bc (diff)
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RAS/CEC: Fix binary search function
commit f3c74b38a55aefe1004200d15a83f109b510068c upstream. Switch to using Donald Knuth's binary search algorithm (The Art of Computer Programming, vol. 3, section 6.2.1). This should've been done from the very beginning but the author must've been smoking something very potent at the time. The problem with the current one was that it would return the wrong element index in certain situations: https://lkml.kernel.org/r/CAM_iQpVd02zkVJ846cj-Fg1yUNuz6tY5q1Vpj4LrXmE06dPYYg@mail.gmail.com and the noodling code after the loop was fishy at best. So switch to using Knuth's binary search. The final result is much cleaner and straightforward. Fixes: 011d82611172 ("RAS: Add a Corrected Errors Collector") Reported-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: Borislav Petkov <bp@suse.de> Cc: Tony Luck <tony.luck@intel.com> Cc: linux-edac <linux-edac@vger.kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
-rw-r--r--drivers/ras/cec.c34
1 files changed, 20 insertions, 14 deletions
diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
index fb0e41e05b72..f85d6b7a1984 100644
--- a/drivers/ras/cec.c
+++ b/drivers/ras/cec.c
@@ -181,32 +181,38 @@ static void cec_work_fn(struct work_struct *work)
*/
static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
{
+ int min = 0, max = ca->n - 1;
u64 this_pfn;
- int min = 0, max = ca->n;
- while (min < max) {
- int tmp = (max + min) >> 1;
+ while (min <= max) {
+ int i = (min + max) >> 1;
- this_pfn = PFN(ca->array[tmp]);
+ this_pfn = PFN(ca->array[i]);
if (this_pfn < pfn)
- min = tmp + 1;
+ min = i + 1;
else if (this_pfn > pfn)
- max = tmp;
- else {
- min = tmp;
- break;
+ max = i - 1;
+ else if (this_pfn == pfn) {
+ if (to)
+ *to = i;
+
+ return i;
}
}
+ /*
+ * When the loop terminates without finding @pfn, min has the index of
+ * the element slot where the new @pfn should be inserted. The loop
+ * terminates when min > max, which means the min index points to the
+ * bigger element while the max index to the smaller element, in-between
+ * which the new @pfn belongs to.
+ *
+ * For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3.
+ */
if (to)
*to = min;
- this_pfn = PFN(ca->array[min]);
-
- if (this_pfn == pfn)
- return min;
-
return -ENOKEY;
}