4.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michal Koutný <mkoutny@xxxxxxxx> commit 1ca0b605150501b7dc59f3016271da4eb3e96fce upstream. One PID may appear multiple times in a preloaded pidlist. (Possibly due to PID recycling but we have reports of the same task_struct appearing with different PIDs, thus possibly involving transfer of PID via de_thread().) Because v1 seq_file iterator uses PIDs as position, it leads to a message: > seq_file: buggy .next function kernfs_seq_next did not update position index Conservative and quick fix consists of removing duplicates from `tasks` file (as opposed to removing pidlists altogether). It doesn't affect correctness (it's sufficient to show a PID once), performance impact would be hidden by unconditional sorting of the pidlist already in place (asymptotically). Link: https://lore.kernel.org/r/20230823174804.23632-1-mkoutny@xxxxxxxx/ Suggested-by: Firo Yang <firo.yang@xxxxxxxx> Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/cgroup/cgroup-v1.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -395,10 +395,9 @@ static int pidlist_array_load(struct cgr } css_task_iter_end(&it); length = n; - /* now sort & (if procs) strip out duplicates */ + /* now sort & strip out duplicates (tgids or recycled thread PIDs) */ sort(array, length, sizeof(pid_t), cmppid, NULL); - if (type == CGROUP_FILE_PROCS) - length = pidlist_uniq(array, length); + length = pidlist_uniq(array, length); l = cgroup_pidlist_find_create(cgrp, type); if (!l) {
