cgroup: prevent spurious transition into non-frozen state

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If freezing of a cgroup races with waking of a task from
the frozen state (like waiting in vfork() or in do_signal_stop()),
a spurious transition of the cgroup state can happen.

The task enters cgroup_leave_frozen(true), the cgroup->nr_frozen_tasks
counter decrements, and the cgroup is switched to the unfrozen state.

To prevent it, let's reserve cgroup_leave_frozen(true) for
terminating processes and use cgroup_leave_frozen(false) otherwise.

To avoid busy-looping in the signal handling loop waiting
for JOBCTL_TRAP_FREEZE set from the cgroup freezing path,
let's do it explicitly in cgroup_leave_frozen(), if the task
is going to stay frozen.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

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This commit is contained in:

Roman Gushchin 2019-04-26 10:59:44 -07:00 • committed by Tejun Heo

parent 533307dc20

commit cb2c4cd878

2 changed files with 6 additions and 12 deletions

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16

kernel/cgroup/freezer.c

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2

kernel/signal.c

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