Quoting Jeff Liu (jeff.liu@xxxxxxxxxx):
> Hello,
>
> Currently, the pid list shown on cgroup->procs & tasks is in ascending order. However, this list is not
> guaranteed to be sorted according to the following records mentioned at Documentation/cgroups/cgroups.txt.
>
> - tasks: list of tasks (by PID) attached to that cgroup. This list
> is not guaranteed to be sorted.
> - cgroup.procs: list of thread group IDs in the cgroup. This list is
> not guaranteed to be sorted or free of duplicate TGIDs, and userspace
> should sort/uniquify the list if this property is required.
>
> This patch remove the sorting function to make the default behavior of pid list be consistent with
> the document.
>
> Without patch:
> # echo 2942 >> /cgroup/test/tasks
> # echo 2803 >> /cgroup/test/tasks
> # echo 2911 >> /cgroup/test/tasks
> # echo 2761 >> /cgroup/test/tasks
> # cat /cgroup/test/tasks
> 2761
> 2803
> 2911
> 2942
> # cat /cgroup/test/cgroup.procs
> 2761
> 2803
> 2911
> 2942
>
> Patch applied:
> # echo 3042 >> /cgroup/testfixed/tasks
> # echo 2916 >> /cgroup/testfixed/tasks
> # echo 2781 >> /cgroup/testfixed/tasks
> # echo 2527 >> /cgroup/testfixed/tasks
> # cat /cgroup/testfixed/tasks
> 2916
> 3042
> 2527
> 2781
> # cat /cgroup/testfixed/cgroup.procs
> 2916
> 3042
> 2527
> 2781
>
>
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
>
> ---
> kernel/cgroup.c | 9 +--------
> 1 file changed, 1 insertion(+), 8 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index f24f724..2b5b477 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -47,7 +47,6 @@
> #include <linux/magic.h>
> #include <linux/spinlock.h>
> #include <linux/string.h>
> -#include <linux/sort.h>
> #include <linux/kmod.h>
> #include <linux/module.h>
> #include <linux/delayacct.h>
> @@ -3374,11 +3373,6 @@ after:
> return dest;
> }
>
> -static int cmppid(const void *a, const void *b)
> -{
> - return *(pid_t *)a - *(pid_t *)b;
> -}
> -
> /*
> * find the appropriate pidlist for our purpose (given procs vs tasks)
> * returns with the lock on that pidlist already held, and takes care
> @@ -3463,8 +3457,7 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
> }
> cgroup_iter_end(cgrp, &it);
> length = n;
> - /* now sort & (if procs) strip out duplicates */
> - sort(array, length, sizeof(pid_t), cmppid, NULL);
> + /* if procs, strip out duplicates */
> if (type == CGROUP_FILE_PROCS)
> length = pidlist_uniq(&array, length);
But... pidlist_uniq() depends on array being sorted
-serge
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