Tejun Heo (tj@xxxxxxxxxx) wrote:
> 61d1d219c4 "cgroup: remove extra calls to find_existing_css_set" made
> cgroup_task_migrate() return void. An unfortunate side effect was
> that cgroup_attach_task() was depending on that function's return
> value to clear its @retval on the success path. On cgroup mounts
> without any subsystem with ->can_attach() callback,
> cgroup_attach_task() ended up returning @retval without initializing
> it on success.
>
> For some reason, gcc failed to warn about it and it didn't cause
> cgroup_attach_task() to return non-zero value in many cases, probably
> due to difference in register allocation. When the problem
> materializes, systemd fails to populate /systemd cgroup mount and
> fails to boot.
>
> Fix it by initializing @retval to zero on declaration.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
> Reported-by: Jiri Kosina <jkosina@xxxxxxx>
> LKML-Reference: <alpine.LNX.2.00.1203282354440.25526@xxxxxxxxxxxxx>
> ---
> Jiri, can you please confirm the fix?
>
> Thanks.
>
> kernel/cgroup.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index f4ea4b6..ed64cca 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1883,7 +1883,7 @@ static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
> */
> int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> {
> - int retval;
> + int retval = 0;
> struct cgroup_subsys *ss, *failed_ss = NULL;
> struct cgroup *oldcgrp;
> struct cgroupfs_root *root = cgrp->root;
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