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pid: fix lockdep deadlock warning due to ucount_lock
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[ INFO: possible irq lock inversion dependency detected ]
4.10.0-rc2-00024-g4aecec9-dirty torvalds#118 Tainted: G        W
---------------------------------------------------------
swapper/1/0 just changed the state of lock:
 (&(&sighand->siglock)->rlock){-.....}, at: [<ffffffffbd0a1bc6>] __lock_task_sighand+0xb6/0x2c0
but this lock took another, HARDIRQ-unsafe lock in the past:
 (ucounts_lock){+.+...}
and interrupts could create inverse lock ordering between them.
other info that might help us debug this:
Chain exists of:                 &(&sighand->siglock)->rlock --> &(&tty->ctrl_lock)->rlock --> ucounts_lock
 Possible interrupt unsafe locking scenario:
       CPU0                    CPU1
       ----                    ----
  lock(ucounts_lock);
                               local_irq_disable();
                               lock(&(&sighand->siglock)->rlock);
                               lock(&(&tty->ctrl_lock)->rlock);
  <Interrupt>
    lock(&(&sighand->siglock)->rlock);

 *** DEADLOCK ***

This patch removes a dependency between rlock and ucount_lock.

Fixes: f333c70 ("pidns: Add a limit on the number of pid namespaces")
Cc: stable@vger.kernel.org
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
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avagin authored and ebiederm committed Jan 10, 2017
1 parent 7542272 commit add7c65
Showing 1 changed file with 6 additions and 4 deletions.
10 changes: 6 additions & 4 deletions kernel/pid_namespace.c
Original file line number Diff line number Diff line change
Expand Up @@ -151,8 +151,12 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns

static void delayed_free_pidns(struct rcu_head *p)
{
kmem_cache_free(pid_ns_cachep,
container_of(p, struct pid_namespace, rcu));
struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);

dec_pid_namespaces(ns->ucounts);
put_user_ns(ns->user_ns);

kmem_cache_free(pid_ns_cachep, ns);
}

static void destroy_pid_namespace(struct pid_namespace *ns)
Expand All @@ -162,8 +166,6 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
ns_free_inum(&ns->ns);
for (i = 0; i < PIDMAP_ENTRIES; i++)
kfree(ns->pidmap[i].page);
dec_pid_namespaces(ns->ucounts);
put_user_ns(ns->user_ns);
call_rcu(&ns->rcu, delayed_free_pidns);
}

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