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Subject[PATCH 2/3] cgroup: pids: kill pids_fork(), simplify pids_can_fork() and pids_cancel_fork()
Now that we know that the forking task can't migrate amd the child is always
moved to the same cgroup by cgroup_post_fork()->css_set_move_task() we can
change pids_can_fork() and pids_cancel_fork() to just use task_css(current).
And since we no longer need to pin this css, we can remove pid_fork().

Note: the patch uses task_css_check(true), perhaps it makes sense to add a
helper or change task_css_set_check() to take cgroup_threadgroup_rwsem into
account.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/cgroup_pids.c | 41 ++++++++++-------------------------------
1 files changed, 10 insertions(+), 31 deletions(-)

diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
index 15ef2e4..de3359a 100644
--- a/kernel/cgroup_pids.c
+++ b/kernel/cgroup_pids.c
@@ -205,48 +205,28 @@ static void pids_cancel_attach(struct cgroup_subsys_state *css,
}
}

+/*
+ * task_css_check(true) in pids_can_fork() and pids_cancel_fork() relies
+ * on threadgroup_change_begin() held by the copy_process().
+ */
static int pids_can_fork(struct task_struct *task, void **priv_p)
{
struct cgroup_subsys_state *css;
struct pids_cgroup *pids;
- int err;

- /*
- * Use the "current" task_css for the pids subsystem as the tentative
- * css. It is possible we will charge the wrong hierarchy, in which
- * case we will forcefully revert/reapply the charge on the right
- * hierarchy after it is committed to the task proper.
- */
- css = task_get_css(current, pids_cgrp_id);
+ css = task_css_check(current, pids_cgrp_id, true);
pids = css_pids(css);
-
- err = pids_try_charge(pids, 1);
- if (err)
- goto err_css_put;
-
- *priv_p = css;
- return 0;
-
-err_css_put:
- css_put(css);
- return err;
+ return pids_try_charge(pids, 1);
}

static void pids_cancel_fork(struct task_struct *task, void *priv)
{
- struct cgroup_subsys_state *css = priv;
- struct pids_cgroup *pids = css_pids(css);
+ struct cgroup_subsys_state *css;
+ struct pids_cgroup *pids;

+ css = task_css_check(current, pids_cgrp_id, true);
+ pids = css_pids(css);
pids_uncharge(pids, 1);
- css_put(css);
-}
-
-static void pids_fork(struct task_struct *task, void *priv)
-{
- struct cgroup_subsys_state *css = priv;
-
- WARN_ON(task_css_check(task, pids_cgrp_id, true) != css);
- css_put(css);
}

static void pids_free(struct task_struct *task)
@@ -329,7 +309,6 @@ struct cgroup_subsys pids_cgrp_subsys = {
.cancel_attach = pids_cancel_attach,
.can_fork = pids_can_fork,
.cancel_fork = pids_cancel_fork,
- .fork = pids_fork,
.free = pids_free,
.legacy_cftypes = pids_files,
.dfl_cftypes = pids_files,
--
1.5.5.1


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