4.19-stable review patch. If anyone has any objections, please let me know.
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From: Michal Koutný mkoutny@suse.com
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@suse.com/ Suggested-by: Firo Yang firo.yang@suse.com Signed-off-by: Michal Koutný mkoutny@suse.com Signed-off-by: Tejun Heo tj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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) {