[PATCH v2 4.19 0/3] Backport patches to fix threadgroup_rwsem <-> cpus_read_lock() deadlock

[PATCH v2 4.19 0/3] Backport patches to fix threadgroup_rwsem <-> cpus_read_lock() deadlock

[Cai Xinchen]

I am very sorry. My gcc version is 7.5 and it does not report error.

We have a deadlock problem which can be solved by commit 4f7e7236435ca
("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock").
However, it makes lock order of cpus_read_lock and cpuset_mutex
wrong in v4.19. The call sequence is as follows:
cgroup_procs_write()
        cgroup_procs_write_start()
                get_online_cpus(); // cpus_read_lock()
                percpu_down_write(&cgroup_threadgroup_rwsem)
        cgroup_attach_task
                cgroup_migrate
                        cgroup_migrate_execute
                                ss->attach (cpust_attach)
                                        mutex_lock(&cpuset_mutex)
it seems hard to make cpus_read_lock is locked before
cgroup_threadgroup_rwsem and cpuset_mutex is locked before
cpus_read_lock unless backport the commit d74b27d63a8beb
("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order")

Changes in v2:
        * Add #include <linux/cpu.h> in kernel/cgroup/cgroup.c to
         avoid some compile error.
        * Exchange get_online_cpus() location in cpuset_attach to
         keep cpu_hotplug_lock->cpuset_mutex order, although it will
          be remove by ("cgroup: Fix threadgroup_rwsem <->
         cpus_read_lock() deadlock")

Juri Lelli (1):
  cgroup/cpuset: Change cpuset_rwsem and hotplug lock order

Tejun Heo (1):
  cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock

Tetsuo Handa (1):
  cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()

 include/linux/cpuset.h    |  8 +++----
 kernel/cgroup/cgroup-v1.c |  3 +++
 kernel/cgroup/cgroup.c    | 50 +++++++++++++++++++++++++++++++++++----
 kernel/cgroup/cpuset.c    | 25 ++++++++++++--------
 4 files changed, 67 insertions(+), 19 deletions(-)

-- 
2.17.1

[PATCH v2 4.19 1/3] cgroup/cpuset: Change cpuset_rwsem and hotplug lock order

[Cai Xinchen]

From: Juri Lelli <juri.lelli@redhat.com>

commit d74b27d63a8bebe2fe634944e4ebdc7b10db7a39 upstream.

commit 1243dc518c9da ("cgroup/cpuset: Convert cpuset_mutex to
percpu_rwsem") is performance patch which is not backport. So
convert percpu_rwsem to cpuset_mutex.

commit aa44002e7db25 ("cpuset: Fix unsafe lock order between
cpuset lock and cpuslock") makes lock order keep cpuset_mutex
->cpu_hotplug_lock. We should change lock order in cpuset_attach.

original commit message:

cpuset_rwsem is going to be acquired from sched_setscheduler() with a
following patch. There are however paths (e.g., spawn_ksoftirqd) in
which sched_scheduler() is eventually called while holding hotplug lock;
this creates a dependecy between hotplug lock (to be always acquired
first) and cpuset_rwsem (to be always acquired after hotplug lock).

Fix paths which currently take the two locks in the wrong order (after
a following patch is applied).

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Cc: claudio@evidence.eu.com
Cc: lizefan@huawei.com
Cc: longman@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: mathieu.poirier@linaro.org
Cc: rostedt@goodmis.org
Cc: tj@kernel.org
Cc: tommaso.cucinotta@santannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-7-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
---
v2:
 * Change get_online_cpus/put_online_cpus lock order in cpuset_attach
   to keep cpuset_mutex and hotplug lock order
---
 include/linux/cpuset.h |  8 ++++----
 kernel/cgroup/cpuset.c | 24 +++++++++++++++++-------
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 934633a05d20..7f1478c26a33 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -40,14 +40,14 @@ static inline bool cpusets_enabled(void)
 
 static inline void cpuset_inc(void)
 {
-	static_branch_inc(&cpusets_pre_enable_key);
-	static_branch_inc(&cpusets_enabled_key);
+	static_branch_inc_cpuslocked(&cpusets_pre_enable_key);
+	static_branch_inc_cpuslocked(&cpusets_enabled_key);
 }
 
 static inline void cpuset_dec(void)
 {
-	static_branch_dec(&cpusets_enabled_key);
-	static_branch_dec(&cpusets_pre_enable_key);
+	static_branch_dec_cpuslocked(&cpusets_enabled_key);
+	static_branch_dec_cpuslocked(&cpusets_pre_enable_key);
 }
 
 extern int cpuset_init(void);
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index dcd5755b1fe2..7169e47fb48b 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -830,8 +830,8 @@ static void rebuild_sched_domains_locked(void)
 	cpumask_var_t *doms;
 	int ndoms;
 
+	lockdep_assert_cpus_held();
 	lockdep_assert_held(&cpuset_mutex);
-	get_online_cpus();
 
 	/*
 	 * We have raced with CPU hotplug. Don't do anything to avoid
@@ -839,15 +839,13 @@ static void rebuild_sched_domains_locked(void)
 	 * Anyways, hotplug work item will rebuild sched domains.
 	 */
 	if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
-		goto out;
+		return;
 
 	/* Generate domain masks and attrs */
 	ndoms = generate_sched_domains(&doms, &attr);
 
 	/* Have scheduler rebuild the domains */
 	partition_sched_domains(ndoms, doms, attr);
-out:
-	put_online_cpus();
 }
 #else /* !CONFIG_SMP */
 static void rebuild_sched_domains_locked(void)
@@ -857,9 +855,11 @@ static void rebuild_sched_domains_locked(void)
 
 void rebuild_sched_domains(void)
 {
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 	rebuild_sched_domains_locked();
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 }
 
 /**
@@ -1528,13 +1528,13 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	cgroup_taskset_first(tset, &css);
 	cs = css_cs(css);
 
-	mutex_lock(&cpuset_mutex);
-
 	/*
 	 * It should hold cpus lock because a cpu offline event can
 	 * cause set_cpus_allowed_ptr() failed.
 	 */
 	get_online_cpus();
+	mutex_lock(&cpuset_mutex);
+
 	/* prepare for attach */
 	if (cs == &top_cpuset)
 		cpumask_copy(cpus_attach, cpu_possible_mask);
@@ -1553,7 +1553,6 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
 		cpuset_update_task_spread_flag(cs, task);
 	}
-       put_online_cpus();
 
 	/*
 	 * Change mm for all threadgroup leaders. This is expensive and may
@@ -1589,6 +1588,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 		wake_up(&cpuset_attach_wq);
 
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 }
 
 /* The various types of files and directories in a cpuset file system */
@@ -1617,6 +1617,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
 	cpuset_filetype_t type = cft->private;
 	int retval = 0;
 
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs)) {
 		retval = -ENODEV;
@@ -1654,6 +1655,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
 	}
 out_unlock:
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 	return retval;
 }
 
@@ -1664,6 +1666,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
 	cpuset_filetype_t type = cft->private;
 	int retval = -ENODEV;
 
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs))
 		goto out_unlock;
@@ -1678,6 +1681,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
 	}
 out_unlock:
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 	return retval;
 }
 
@@ -1716,6 +1720,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 	kernfs_break_active_protection(of->kn);
 	flush_work(&cpuset_hotplug_work);
 
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs))
 		goto out_unlock;
@@ -1741,6 +1746,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 	free_trial_cpuset(trialcs);
 out_unlock:
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 	kernfs_unbreak_active_protection(of->kn);
 	css_put(&cs->css);
 	flush_workqueue(cpuset_migrate_mm_wq);
@@ -1985,6 +1991,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 	if (!parent)
 		return 0;
 
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 
 	set_bit(CS_ONLINE, &cs->flags);
@@ -2035,6 +2042,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 	spin_unlock_irq(&callback_lock);
 out_unlock:
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 	return 0;
 }
 
@@ -2048,6 +2056,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
 {
 	struct cpuset *cs = css_cs(css);
 
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 
 	if (is_sched_load_balance(cs))
@@ -2057,6 +2066,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
 	clear_bit(CS_ONLINE, &cs->flags);
 
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 }
 
 static void cpuset_css_free(struct cgroup_subsys_state *css)
-- 
2.17.1

[PATCH v2 4.19 2/3] cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock

[Cai Xinchen]

From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

commit 4f7e7236435ca0abe005c674ebd6892c6e83aeb3 upstream.

Add #include <linux/cpu.h> to avoid compile error on some architectures.

commit 9a3284fad42f6 ("cgroup: Optimize single thread migration") and
commit 671c11f0619e5 ("cgroup: Elide write-locking threadgroup_rwsem
when updating csses on an empty subtree") are not backport. So ignore the
input parameter of cgroup_attach_lock/cgroup_attach_unlock.

original commit message:

Bringing up a CPU may involve creating and destroying tasks which requires
read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside
cpus_read_lock(). However, cpuset's ->attach(), which may be called with
thredagroup_rwsem write-locked, also wants to disable CPU hotplug and
acquires cpus_read_lock(), leading to a deadlock.

Fix it by guaranteeing that ->attach() is always called with CPU hotplug
disabled and removing cpus_read_lock() call from cpuset_attach().

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Reviewed-and-tested-by: Imran Khan <imran.f.khan-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
Reported-and-tested-by: Xuewen Yan <xuewen.yan-1tVvrHeaX6nQT0dZR+AlfA@public.gmane.org>
Fixes: 05c7b7a92cc8 ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug")
Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org # v5.17+
Signed-off-by: Cai Xinchen <caixinchen1-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
v2:
 - Add #include <linux/cpu.h> in kernel/cgroup/cgroup.c to avoid compile
   error on some architectures
---
 kernel/cgroup/cgroup.c | 50 +++++++++++++++++++++++++++++++++++++-----
 kernel/cgroup/cpuset.c |  7 +-----
 2 files changed, 46 insertions(+), 11 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index a892a99eb4bf..a8185cdb8587 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -55,6 +55,7 @@
 #include <linux/nsproxy.h>
 #include <linux/file.h>
 #include <linux/sched/cputime.h>
+#include <linux/cpu.h>
 #include <net/sock.h>
 
 #define CREATE_TRACE_POINTS
@@ -2209,6 +2210,45 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 }
 EXPORT_SYMBOL_GPL(task_cgroup_path);
 
+/**
+ * cgroup_attach_lock - Lock for ->attach()
+ * @lock_threadgroup: whether to down_write cgroup_threadgroup_rwsem
+ *
+ * cgroup migration sometimes needs to stabilize threadgroups against forks and
+ * exits by write-locking cgroup_threadgroup_rwsem. However, some ->attach()
+ * implementations (e.g. cpuset), also need to disable CPU hotplug.
+ * Unfortunately, letting ->attach() operations acquire cpus_read_lock() can
+ * lead to deadlocks.
+ *
+ * Bringing up a CPU may involve creating and destroying tasks which requires
+ * read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside
+ * cpus_read_lock(). If we call an ->attach() which acquires the cpus lock while
+ * write-locking threadgroup_rwsem, the locking order is reversed and we end up
+ * waiting for an on-going CPU hotplug operation which in turn is waiting for
+ * the threadgroup_rwsem to be released to create new tasks. For more details:
+ *
+ *   http://lkml.kernel.org/r/20220711174629.uehfmqegcwn2lqzu@wubuntu
+ *
+ * Resolve the situation by always acquiring cpus_read_lock() before optionally
+ * write-locking cgroup_threadgroup_rwsem. This allows ->attach() to assume that
+ * CPU hotplug is disabled on entry.
+ */
+static void cgroup_attach_lock(void)
+{
+	get_online_cpus();
+	percpu_down_write(&cgroup_threadgroup_rwsem);
+}
+
+/**
+ * cgroup_attach_unlock - Undo cgroup_attach_lock()
+ * @lock_threadgroup: whether to up_write cgroup_threadgroup_rwsem
+ */
+static void cgroup_attach_unlock(void)
+{
+	percpu_up_write(&cgroup_threadgroup_rwsem);
+	put_online_cpus();
+}
+
 /**
  * cgroup_migrate_add_task - add a migration target task to a migration context
  * @task: target task
@@ -2694,7 +2734,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
 	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
 		return ERR_PTR(-EINVAL);
 
-	percpu_down_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_lock();
 
 	rcu_read_lock();
 	if (pid) {
@@ -2725,7 +2765,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
 	goto out_unlock_rcu;
 
 out_unlock_threadgroup:
-	percpu_up_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_unlock();
 out_unlock_rcu:
 	rcu_read_unlock();
 	return tsk;
@@ -2740,7 +2780,7 @@ void cgroup_procs_write_finish(struct task_struct *task)
 	/* release reference from cgroup_procs_write_start() */
 	put_task_struct(task);
 
-	percpu_up_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_unlock();
 	for_each_subsys(ss, ssid)
 		if (ss->post_attach)
 			ss->post_attach();
@@ -2799,7 +2839,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
 
 	lockdep_assert_held(&cgroup_mutex);
 
-	percpu_down_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_lock();
 
 	/* look up all csses currently attached to @cgrp's subtree */
 	spin_lock_irq(&css_set_lock);
@@ -2830,7 +2870,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
 	ret = cgroup_migrate_execute(&mgctx);
 out_finish:
 	cgroup_migrate_finish(&mgctx);
-	percpu_up_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_unlock();
 	return ret;
 }
 
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7169e47fb48b..c6d412cebc43 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1528,11 +1528,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	cgroup_taskset_first(tset, &css);
 	cs = css_cs(css);
 
-	/*
-	 * It should hold cpus lock because a cpu offline event can
-	 * cause set_cpus_allowed_ptr() failed.
-	 */
-	get_online_cpus();
+	lockdep_assert_cpus_held();     /* see cgroup_attach_lock() */
 	mutex_lock(&cpuset_mutex);
 
 	/* prepare for attach */
@@ -1588,7 +1584,6 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 		wake_up(&cpuset_attach_wq);
 
 	mutex_unlock(&cpuset_mutex);
-	put_online_cpus();
 }
 
 /* The various types of files and directories in a cpuset file system */
-- 
2.17.1

Re: [PATCH v2 4.19 0/3] Backport patches to fix threadgroup_rwsem <-> cpus_read_lock() deadlock

[Greg KH]

On Mon, Mar 20, 2023 at 01:15:04AM +0000, Cai Xinchen wrote:
> I am very sorry. My gcc version is 7.5 and it does not report error.
> 
> We have a deadlock problem which can be solved by commit 4f7e7236435ca
> ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock").
> However, it makes lock order of cpus_read_lock and cpuset_mutex
> wrong in v4.19. The call sequence is as follows:
> cgroup_procs_write()
>         cgroup_procs_write_start()
>                 get_online_cpus(); // cpus_read_lock()
>                 percpu_down_write(&cgroup_threadgroup_rwsem)
>         cgroup_attach_task
>                 cgroup_migrate
>                         cgroup_migrate_execute
>                                 ss->attach (cpust_attach)
>                                         mutex_lock(&cpuset_mutex)
> it seems hard to make cpus_read_lock is locked before
> cgroup_threadgroup_rwsem and cpuset_mutex is locked before
> cpus_read_lock unless backport the commit d74b27d63a8beb
> ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order")
> 
> Changes in v2:
>         * Add #include <linux/cpu.h> in kernel/cgroup/cgroup.c to
>          avoid some compile error.
>         * Exchange get_online_cpus() location in cpuset_attach to
>          keep cpu_hotplug_lock->cpuset_mutex order, although it will
>           be remove by ("cgroup: Fix threadgroup_rwsem <->
>          cpus_read_lock() deadlock")
> 
> Juri Lelli (1):
>   cgroup/cpuset: Change cpuset_rwsem and hotplug lock order
> 
> Tejun Heo (1):
>   cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock
> 
> Tetsuo Handa (1):
>   cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()
> 
>  include/linux/cpuset.h    |  8 +++----
>  kernel/cgroup/cgroup-v1.c |  3 +++
>  kernel/cgroup/cgroup.c    | 50 +++++++++++++++++++++++++++++++++++----
>  kernel/cgroup/cpuset.c    | 25 ++++++++++++--------
>  4 files changed, 67 insertions(+), 19 deletions(-)

Now queued up, thanks.

greg k-h

[PATCH v2 4.19 3/3] cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()

[Cai Xinchen]

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit 43626dade36fa74d3329046f4ae2d7fdefe401c6 upstream.

syzbot is hitting percpu_rwsem_assert_held(&cpu_hotplug_lock) warning at
cpuset_attach() [1], for commit 4f7e7236435ca0ab ("cgroup: Fix
threadgroup_rwsem <-> cpus_read_lock() deadlock") missed that
cpuset_attach() is also called from cgroup_attach_task_all().
Add cpus_read_lock() like what cgroup_procs_write_start() does.

Link: https://syzkaller.appspot.com/bug?extid=29d3a3b4d86c8136ad9e [1]
Reported-by: syzbot <syzbot+29d3a3b4d86c8136ad9e@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 4f7e7236435ca0ab ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock")
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
---
 kernel/cgroup/cgroup-v1.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 61644976225a..c0ebb70808b6 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -13,6 +13,7 @@
 #include <linux/delayacct.h>
 #include <linux/pid_namespace.h>
 #include <linux/cgroupstats.h>
+#include <linux/cpu.h>
 
 #include <trace/events/cgroup.h>
 
@@ -55,6 +56,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
+	get_online_cpus();
 	percpu_down_write(&cgroup_threadgroup_rwsem);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
@@ -71,6 +73,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 			break;
 	}
 	percpu_up_write(&cgroup_threadgroup_rwsem);
+	put_online_cpus();
 	mutex_unlock(&cgroup_mutex);
 
 	return retval;
-- 
2.17.1