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author | Roman Gushchin <guro@fb.com> | 2019-04-26 10:59:44 -0700 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2019-05-06 08:39:06 -0700 |
commit | cb2c4cd87874a7975b7b8615866b3a87bae10aab (patch) | |
tree | 306f73b6b4208a222e4e8e3902d5de62668eb5cb | |
parent | 533307dc20a9e84a0687d4ca24aeb669516c0243 (diff) | |
download | linux-stable-cb2c4cd87874a7975b7b8615866b3a87bae10aab.tar.gz linux-stable-cb2c4cd87874a7975b7b8615866b3a87bae10aab.tar.bz2 linux-stable-cb2c4cd87874a7975b7b8615866b3a87bae10aab.zip |
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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r-- | kernel/cgroup/freezer.c | 16 | ||||
-rw-r--r-- | kernel/signal.c | 2 |
2 files changed, 6 insertions, 12 deletions
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c index 3bfbb3c8baf3..c321e768f8d3 100644 --- a/kernel/cgroup/freezer.c +++ b/kernel/cgroup/freezer.c @@ -139,19 +139,13 @@ void cgroup_leave_frozen(bool always_leave) cgroup_update_frozen(cgrp); WARN_ON_ONCE(!current->frozen); current->frozen = false; + } else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) { + spin_lock(¤t->sighand->siglock); + current->jobctl |= JOBCTL_TRAP_FREEZE; + set_thread_flag(TIF_SIGPENDING); + spin_unlock(¤t->sighand->siglock); } 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(¤t->sighand->siglock); - recalc_sigpending(); - spin_unlock_irq(¤t->sighand->siglock); - } } /* diff --git a/kernel/signal.c b/kernel/signal.c index 095e0fc57b25..16b72f4f14df 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2514,7 +2514,7 @@ relock: */ if (unlikely(cgroup_task_frozen(current))) { spin_unlock_irq(&sighand->siglock); - cgroup_leave_frozen(true); + cgroup_leave_frozen(false); goto relock; } |