[PATCH 2/2] drmgr: Remove only available LMBs from CPU less NUMA node

[Haren Myneni]

The current logic in remove_cpuless_lmbs() may remove more LMB
than requested.

todo = (count * node->ratio) / 100; --> can be 0
todo = min(todo, node->n_lmbs);
if (!todo && node->n_lmbs)
todo = (count - this_loop); -> todo may be > node->n_lmbs

Removing more lmbs than requested caused a decrement of count
(unsigned int) integer overflow, eventually leading to the drmgr
removing all available memory in the system. Existing testing
exposed the out of memory issue triggered by this counter
overflow.

This patch fixed this logic by adjusting todo per node dynamically
based on the count value and then determine todo value based on
number of available LMBs in the node.

Signed-off-by: Ryan Whittaker <ryan...@linux.ibm.com>
Reviewed-by: Mingming Cao <m...@linux.ibm.com>
Signed-off-by: Haren Myneni <ha...@linux.ibm.com>
---
src/drmgr/drslot_chrp_mem.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/drmgr/drslot_chrp_mem.c b/src/drmgr/drslot_chrp_mem.c
index 179fb17..4a36c73 100644
--- a/src/drmgr/drslot_chrp_mem.c
+++ b/src/drmgr/drslot_chrp_mem.c
@@ -1565,11 +1565,16 @@ static int remove_cpuless_lmbs(uint32_t count)
continue;

todo = (count * node->ratio) / 100;
- todo = min(todo, node->n_lmbs);
- /* Fix rounded value to 0 */
- if (!todo && node->n_lmbs)
+ /*
+ * Fix rounded value to 0 and fix if a 0 ratio has
+ * been processed
+ */
+ if ((!todo && node->n_lmbs) || (count - this_loop < todo))
todo = (count - this_loop);

+ /* Donot request more than available */
+ todo = min(todo, node->n_lmbs);
+
if (todo)
todo = remove_lmb_from_node(node, todo);

@@ -1583,7 +1588,13 @@ static int remove_cpuless_lmbs(uint32_t count)
if (!this_loop)
break;

- count -= this_loop;
+ /*
+ * Should not happen, but in case prevent integer overflow
+ */
+ if (this_loop < count)
+ count -= this_loop;
+ else
+ count = 0;
}

say(DEBUG, "%d / %d LMBs removed from the CPU less nodes\n",
--
2.50.1