From add7c65ca426b7a37184dd3d2172394e23d585d6 Mon Sep 17 00:00:00 2001 From: Andrei Vagin Date: Wed, 4 Jan 2017 19:28:14 -0800 Subject: [PATCH] pid: fix lockdep deadlock warning due to ucount_lock ========================================================= [ INFO: possible irq lock inversion dependency detected ] 4.10.0-rc2-00024-g4aecec9-dirty #118 Tainted: G W --------------------------------------------------------- swapper/1/0 just changed the state of lock: (&(&sighand->siglock)->rlock){-.....}, at: [] __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); lock(&(&sighand->siglock)->rlock); *** DEADLOCK *** This patch removes a dependency between rlock and ucount_lock. Fixes: f333c700c610 ("pidns: Add a limit on the number of pid namespaces") Cc: stable@vger.kernel.org Signed-off-by: Andrei Vagin Acked-by: Al Viro Signed-off-by: Eric W. Biederman --- kernel/pid_namespace.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index df9e8e9e0be7..eef2ce968636 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -151,8 +151,12 @@ out: 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) @@ -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); } -- 2.20.1