Oleg Nesterov d0bc74c563 cgroup/pids: turn cgroup_subsys->free() into cgroup_subsys->release() to fix the accounting ... [ Upstream commit 51bee5abea ] The only user of cgroup_subsys->free() callback is pids_cgrp_subsys which needs pids_free() to uncharge the pid. However, ->free() is called from __put_task_struct()->cgroup_free() and this is too late. Even the trivial program which does for (;;) { int pid = fork(); assert(pid >= 0); if (pid) wait(NULL); else exit(0); } can run out of limits because release_task()->call_rcu(delayed_put_task_struct) implies an RCU gp after the task/pid goes away and before the final put(). Test-case: mkdir -p /tmp/CG mount -t cgroup2 none /tmp/CG echo '+pids' > /tmp/CG/cgroup.subtree_control mkdir /tmp/CG/PID echo 2 > /tmp/CG/PID/pids.max perl -e 'while ($p = fork) { wait; } $p // die "fork failed: $!\n"' & echo $! > /tmp/CG/PID/cgroup.procs Without this patch the forking process fails soon after migration. Rename cgroup_subsys->free() to cgroup_subsys->release() and move the callsite into the new helper, cgroup_release(), called by release_task() which actually frees the pid(s). Reported-by: Herton R. Krzesinski <hkrzesin@redhat.com> Reported-by: Jan Stancek <jstancek@redhat.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2019-04-05 22:33:13 +02:00
..
Makefile	cgroup: Rename kernel/cgroup/stat.c to kernel/cgroup/rstat.c	2018-04-26 14:29:04 -07:00
cgroup-internal.h	cgroup/tracing: Move taking of spin lock out of trace event handlers	2018-07-11 10:48:47 -07:00
cgroup-v1.c	cgroup/tracing: Move taking of spin lock out of trace event handlers	2018-07-11 10:48:47 -07:00
cgroup.c	cgroup/pids: turn cgroup_subsys->free() into cgroup_subsys->release() to fix the accounting	2019-04-05 22:33:13 +02:00
cpuset.c	docs: Fix some broken references	2018-06-15 18:10:01 -03:00
debug.c	debug cgroup: use task_css_set instead of rcu_dereference	2017-11-27 11:37:33 -08:00
freezer.c	cgroup: add @flags to css_task_iter_start() and implement CSS_TASK_ITER_PROCS	2017-07-21 11:14:51 -04:00
namespace.c	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
pids.c	cgroup/pids: turn cgroup_subsys->free() into cgroup_subsys->release() to fix the accounting	2019-04-05 22:33:13 +02:00
rdma.c	rdmacg: Convert to use match_string() helper	2018-05-07 09:27:26 -07:00
rstat.c	cgroup, rstat: Don't flush subtree root unless necessary	2019-04-05 22:33:06 +02:00