7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: SJ Park [ Upstream commit 485a9149ad406e00949327a3231b9084d7073706 ] In an extreme and unlikely situation, si_meminfo_node() might let the caller show zero total ram. That could cause a divide by zero in damon_get_node_mem_bp(). It could also show free memory larger than the total memory. This could cause underflow and make DAMOS temporarily make unexpected behavior. Thanks to safety guards in the auto-tuning feedback loop, that should not be a real problem, though. Fix the problems by respectively returning 100% and 0% for used and free memory queries in the corner cases. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260901131850.98037-7-sj@kernel.org Link: https://lore.kernel.org/20260328133216.9697-1-sj@kernel.org [1] Fixes: 0e1c773b501f ("mm/damon/core: introduce damos quota goal metrics for memory node utilization") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Cc: Usama Arif Cc: # 6.16.x Signed-off-by: Sasha Levin --- mm/damon/core.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index b3390978581a6..c00f1651b04a6 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2829,6 +2829,13 @@ static __kernel_ulong_t damos_get_node_mem_bp( } si_meminfo_node(&i, goal->nid); + if (!i.totalram || i.totalram < i.freeram) { + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) + return 10000; + else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ + return 0; + } + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) numerator = i.totalram - i.freeram; else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ -- 2.53.0