Syzbot reported the following bug: BUG: KCSAN: data-race in mem_cgroup_select_victim_node / mem_cgroup_select_victim_node write to 0xffff88809fade9b0 of 4 bytes by task 8603 on cpu 0: mem_cgroup_select_victim_node+0xb5/0x3d0 mm/memcontrol.c:1686 try_to_free_mem_cgroup_pages+0x175/0x4c0 mm/vmscan.c:3376 reclaim_high.constprop.0+0xf7/0x140 mm/memcontrol.c:2349 mem_cgroup_handle_over_high+0x96/0x180 mm/memcontrol.c:2430 tracehook_notify_resume include/linux/tracehook.h:197 [inline] exit_to_usermode_loop+0x20c/0x2c0 arch/x86/entry/common.c:163 prepare_exit_to_usermode+0x180/0x1a0 arch/x86/entry/common.c:194 swapgs_restore_regs_and_return_to_usermode+0x0/0x40 read to 0xffff88809fade9b0 of 4 bytes by task 7290 on cpu 1: mem_cgroup_select_victim_node+0x92/0x3d0 mm/memcontrol.c:1675 try_to_free_mem_cgroup_pages+0x175/0x4c0 mm/vmscan.c:3376 reclaim_high.constprop.0+0xf7/0x140 mm/memcontrol.c:2349 mem_cgroup_handle_over_high+0x96/0x180 mm/memcontrol.c:2430 tracehook_notify_resume include/linux/tracehook.h:197 [inline] exit_to_usermode_loop+0x20c/0x2c0 arch/x86/entry/common.c:163 prepare_exit_to_usermode+0x180/0x1a0 arch/x86/entry/common.c:194 swapgs_restore_regs_and_return_to_usermode+0x0/0x40 mem_cgroup_select_victim_node() can be called concurrently which reads and modifies memcg->last_scanned_node without any synchrnonization. So, read and modify memcg->last_scanned_node with READ_ONCE()/WRITE_ONCE() to stop potential reordering. Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Greg Thelen <gthelen@xxxxxxxxxx> Reported-by: syzbot+13f93c99c06988391efe@xxxxxxxxxxxxxxxxxxxxxxxxx --- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c4c555055a72..5a06739dd3e4 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1667,7 +1667,7 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg) int node; mem_cgroup_may_update_nodemask(memcg); - node = memcg->last_scanned_node; + node = READ_ONCE(memcg->last_scanned_node); node = next_node_in(node, memcg->scan_nodes); /* @@ -1678,7 +1678,7 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg) if (unlikely(node == MAX_NUMNODES)) node = numa_node_id(); - memcg->last_scanned_node = node; + WRITE_ONCE(memcg->last_scanned_node, node); return node; } #else -- 2.24.0.rc0.303.g954a862665-goog
