* [PATCH 0/2] cgroup v2 freezer follow-up patches
@ 2019-04-26 17:59 Roman Gushchin
2019-04-26 17:59 ` [PATCH 1/2] cgroup: prevent spurious transition into non-frozen state Roman Gushchin
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Roman Gushchin @ 2019-04-26 17:59 UTC (permalink / raw)
To: Tejun Heo
Cc: Oleg Nesterov, kernel-team, cgroups, linux-kernel, Roman Gushchin
Hi, Tejun!
Please, pull these two follow-up patches for the cgroup v2 freezer.
These are a fix for a spurious state transition, which could happen
due to a race condition, and a cleanup of some dead code. Both patches
were suggested by Oleg Nesterov.
Thank you!
Roman Gushchin (2):
cgroup: prevent spurious transition into non-frozen state
cgroup: get rid of cgroup_freezer_frozen_exit()
include/linux/cgroup.h | 2 +-
kernel/cgroup/cgroup.c | 5 ++---
kernel/cgroup/freezer.c | 26 +++++---------------------
kernel/signal.c | 2 +-
4 files changed, 9 insertions(+), 26 deletions(-)
--
2.20.1
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH 1/2] cgroup: prevent spurious transition into non-frozen state
2019-04-26 17:59 [PATCH 0/2] cgroup v2 freezer follow-up patches Roman Gushchin
@ 2019-04-26 17:59 ` Roman Gushchin
2019-04-26 17:59 ` [PATCH 2/2] cgroup: get rid of cgroup_freezer_frozen_exit() Roman Gushchin
2019-05-06 15:40 ` [PATCH 0/2] cgroup v2 freezer follow-up patches Tejun Heo
2 siblings, 0 replies; 4+ messages in thread
From: Roman Gushchin @ 2019-04-26 17:59 UTC (permalink / raw)
To: Tejun Heo
Cc: Oleg Nesterov, kernel-team, cgroups, linux-kernel, Roman Gushchin
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>
---
kernel/cgroup/freezer.c | 16 +++++-----------
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 @@ bool get_signal(struct ksignal *ksig)
*/
if (unlikely(cgroup_task_frozen(current))) {
spin_unlock_irq(&sighand->siglock);
- cgroup_leave_frozen(true);
+ cgroup_leave_frozen(false);
goto relock;
}
--
2.20.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH 2/2] cgroup: get rid of cgroup_freezer_frozen_exit()
2019-04-26 17:59 [PATCH 0/2] cgroup v2 freezer follow-up patches Roman Gushchin
2019-04-26 17:59 ` [PATCH 1/2] cgroup: prevent spurious transition into non-frozen state Roman Gushchin
@ 2019-04-26 17:59 ` Roman Gushchin
2019-05-06 15:40 ` [PATCH 0/2] cgroup v2 freezer follow-up patches Tejun Heo
2 siblings, 0 replies; 4+ messages in thread
From: Roman Gushchin @ 2019-04-26 17:59 UTC (permalink / raw)
To: Tejun Heo
Cc: Oleg Nesterov, kernel-team, cgroups, linux-kernel, Roman Gushchin
A task should never enter the exit path with the task->frozen bit set.
Any frozen task must enter the signal handling loop and the only
way to escape is through cgroup_leave_frozen(true), which
unconditionally drops the task->frozen bit. So it means that
cgroyp_freezer_frozen_exit() has zero chances to be called and
has to be removed.
Let's put a WARN_ON_ONCE() instead of the cgroup_freezer_frozen_exit()
call to catch any potential leak of the task's frozen bit.
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Roman Gushchin <guro@fb.com>
---
include/linux/cgroup.h | 2 +-
kernel/cgroup/cgroup.c | 5 ++---
kernel/cgroup/freezer.c | 10 ----------
3 files changed, 3 insertions(+), 14 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 3e2efd412dfa..c0077adeea83 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -889,7 +889,7 @@ void cgroup_update_frozen(struct cgroup *cgrp);
void cgroup_freeze(struct cgroup *cgrp, bool freeze);
void cgroup_freezer_migrate_task(struct task_struct *task, struct cgroup *src,
struct cgroup *dst);
-void cgroup_freezer_frozen_exit(struct task_struct *task);
+
static inline bool cgroup_task_freeze(struct task_struct *task)
{
bool ret;
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 57edcf398d71..622ae7452969 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5929,9 +5929,8 @@ void cgroup_exit(struct task_struct *tsk)
css_set_move_task(tsk, cset, NULL, false);
cset->nr_tasks--;
- if (unlikely(cgroup_task_frozen(tsk)))
- cgroup_freezer_frozen_exit(tsk);
- else if (unlikely(cgroup_task_freeze(tsk)))
+ WARN_ON_ONCE(cgroup_task_frozen(tsk));
+ if (unlikely(cgroup_task_freeze(tsk)))
cgroup_update_frozen(task_dfl_cgroup(tsk));
spin_unlock_irq(&css_set_lock);
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
index c321e768f8d3..8cf010680678 100644
--- a/kernel/cgroup/freezer.c
+++ b/kernel/cgroup/freezer.c
@@ -248,16 +248,6 @@ void cgroup_freezer_migrate_task(struct task_struct *task,
cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags));
}
-void cgroup_freezer_frozen_exit(struct task_struct *task)
-{
- struct cgroup *cgrp = task_dfl_cgroup(task);
-
- lockdep_assert_held(&css_set_lock);
-
- cgroup_dec_frozen_cnt(cgrp);
- cgroup_update_frozen(cgrp);
-}
-
void cgroup_freeze(struct cgroup *cgrp, bool freeze)
{
struct cgroup_subsys_state *css;
--
2.20.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH 0/2] cgroup v2 freezer follow-up patches
2019-04-26 17:59 [PATCH 0/2] cgroup v2 freezer follow-up patches Roman Gushchin
2019-04-26 17:59 ` [PATCH 1/2] cgroup: prevent spurious transition into non-frozen state Roman Gushchin
2019-04-26 17:59 ` [PATCH 2/2] cgroup: get rid of cgroup_freezer_frozen_exit() Roman Gushchin
@ 2019-05-06 15:40 ` Tejun Heo
2 siblings, 0 replies; 4+ messages in thread
From: Tejun Heo @ 2019-05-06 15:40 UTC (permalink / raw)
To: Roman Gushchin; +Cc: Oleg Nesterov, kernel-team, cgroups, linux-kernel
On Fri, Apr 26, 2019 at 10:59:43AM -0700, Roman Gushchin wrote:
> Hi, Tejun!
>
> Please, pull these two follow-up patches for the cgroup v2 freezer.
>
> These are a fix for a spurious state transition, which could happen
> due to a race condition, and a cleanup of some dead code. Both patches
> were suggested by Oleg Nesterov.
Applied to cgroup/for-5.2.
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 4+ messages in thread
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2019-04-26 17:59 [PATCH 0/2] cgroup v2 freezer follow-up patches Roman Gushchin
2019-04-26 17:59 ` [PATCH 1/2] cgroup: prevent spurious transition into non-frozen state Roman Gushchin
2019-04-26 17:59 ` [PATCH 2/2] cgroup: get rid of cgroup_freezer_frozen_exit() Roman Gushchin
2019-05-06 15:40 ` [PATCH 0/2] cgroup v2 freezer follow-up patches Tejun Heo
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