This is a note to let you know that I've just added the patch titled
cgroup: Remove duplicates in cgroup v1 tasks file
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cgroup-remove-duplicates-in-cgroup-v1-tasks-file.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1ca0b605150501b7dc59f3016271da4eb3e96fce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@xxxxxxxx>
Date: Mon, 9 Oct 2023 15:58:11 +0200
Subject: cgroup: Remove duplicates in cgroup v1 tasks file
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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) {
Patches currently in stable-queue which might be from mkoutny@xxxxxxxx are
queue-4.19/cgroup-remove-duplicates-in-cgroup-v1-tasks-file.patch
