| From 1ca0b605150501b7dc59f3016271da4eb3e96fce Mon Sep 17 00:00:00 2001 |
| From: =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@suse.com> |
| Date: Mon, 9 Oct 2023 15:58:11 +0200 |
| Subject: cgroup: Remove duplicates in cgroup v1 tasks file |
| MIME-Version: 1.0 |
| Content-Type: text/plain; charset=UTF-8 |
| Content-Transfer-Encoding: 8bit |
| |
| 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 |
| @@ -360,10 +360,9 @@ 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) { |
