Commit cb2c4cd8 authored by Roman Gushchin's avatar Roman Gushchin Committed by Tejun Heo

cgroup: prevent spurious transition into non-frozen state

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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 533307dc
...@@ -139,19 +139,13 @@ void cgroup_leave_frozen(bool always_leave) ...@@ -139,19 +139,13 @@ void cgroup_leave_frozen(bool always_leave)
cgroup_update_frozen(cgrp); cgroup_update_frozen(cgrp);
WARN_ON_ONCE(!current->frozen); WARN_ON_ONCE(!current->frozen);
current->frozen = false; current->frozen = false;
} else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) {
spin_lock(&current->sighand->siglock);
current->jobctl |= JOBCTL_TRAP_FREEZE;
set_thread_flag(TIF_SIGPENDING);
spin_unlock(&current->sighand->siglock);
} }
spin_unlock_irq(&css_set_lock); spin_unlock_irq(&css_set_lock);
if (unlikely(current->frozen)) {
/*
* If the task remained in the frozen state,
* make sure it won't reach userspace without
* entering the signal handling loop.
*/
spin_lock_irq(&current->sighand->siglock);
recalc_sigpending();
spin_unlock_irq(&current->sighand->siglock);
}
} }
/* /*
......
...@@ -2514,7 +2514,7 @@ bool get_signal(struct ksignal *ksig) ...@@ -2514,7 +2514,7 @@ bool get_signal(struct ksignal *ksig)
*/ */
if (unlikely(cgroup_task_frozen(current))) { if (unlikely(cgroup_task_frozen(current))) {
spin_unlock_irq(&sighand->siglock); spin_unlock_irq(&sighand->siglock);
cgroup_leave_frozen(true); cgroup_leave_frozen(false);
goto relock; goto relock;
} }
......
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