ipc/namespace.c: use a work queue to free_ipc

the reason is to avoid a delay caused by the synchronize_rcu() call in kern_umount() when the mqueue mount is freed. the code: #define _GNU_SOURCE #include <sched.h> #include <error.h> #include <errno.h> #include <stdlib.h> int main() { int i; for (i = 0; i < 1000; i++) if (unshare(CLONE_NEWIPC) < 0) error(EXIT_FAILURE, errno, "unshare"); } goes from Command being timed: "./ipc-namespace" User time (seconds): 0.00 System time (seconds): 0.06 Percent of CPU this job got: 0% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:08.05 to Command being timed: "./ipc-namespace" User time (seconds): 0.00 System time (seconds): 0.02 Percent of CPU this job got: 96% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.03

Giuseppe Scrivano committed 6 years ago

Commit e1eb26f1 parent 4b78e202 files · +24 −2Browse files

Unified · Split

2 files

include/linux/ipc_namespace.h +2 −0
ipc/namespace.c +22 −2

include/linux/ipc_namespace.h+2−0

@@ -68,6 +68,8 @@ struct ipc_namespace { · 67 unmodified lines
68	struct user_namespace *user_ns;	68	struct user_namespace *user_ns;
69	struct ucounts *ucounts;	69	struct ucounts *ucounts;
70		70
		71	struct llist_node mnt_llist;
		72
71	struct ns_common ns;	73	struct ns_common ns;
72	} __randomize_layout;	74	} __randomize_layout;
73		75

ipc/namespace.c+22−2

@@ -117,6 +117,10 @@ void free_ipcs(struct ipc_namespace ns, struct ipc_ids ids, · 116 unmodified lines
117		117
118	static void free_ipc_ns(struct ipc_namespace *ns)	118	static void free_ipc_ns(struct ipc_namespace *ns)
119	{	119	{
		120	/* mq_put_mnt() waits for a grace period as kern_unmount()
		121	* uses synchronize_rcu().
		122	*/
		123	mq_put_mnt(ns);
120	sem_exit_ns(ns);	124	sem_exit_ns(ns);
121	msg_exit_ns(ns);	125	msg_exit_ns(ns);
122	shm_exit_ns(ns);	126	shm_exit_ns(ns);
@@ -127,6 +131,21 @@ static void free_ipc_ns(struct ipc_namespace *ns) · 4 unmodified lines
127	kfree(ns);	131	kfree(ns);
128	}	132	}
129		133
		134	static LLIST_HEAD(free_ipc_list);
		135	static void free_ipc(struct work_struct *unused)
		136	{
		137	struct llist_node *node = llist_del_all(&free_ipc_list);
		138	struct ipc_namespace n, t;
		139
		140	llist_for_each_entry_safe(n, t, node, mnt_llist)
		141	free_ipc_ns(n);
		142	}
		143
		144	/*
		145	* The work queue is used to avoid the cost of synchronize_rcu in kern_unmount.
		146	*/
		147	static DECLARE_WORK(free_ipc_work, free_ipc);
		148
130	/*	149	/*
131	* put_ipc_ns - drop a reference to an ipc namespace.	150	* put_ipc_ns - drop a reference to an ipc namespace.
132	* @ns: the namespace to put	151	* @ns: the namespace to put
@@ -148,8 +167,9 @@ void put_ipc_ns(struct ipc_namespace *ns) · 15 unmodified lines
148	if (refcount_dec_and_lock(&ns->count, &mq_lock)) {	167	if (refcount_dec_and_lock(&ns->count, &mq_lock)) {
149	mq_clear_sbinfo(ns);	168	mq_clear_sbinfo(ns);
150	spin_unlock(&mq_lock);	169	spin_unlock(&mq_lock);
151	mq_put_mnt(ns);	170
152	free_ipc_ns(ns);	171	if (llist_add(&ns->mnt_llist, &free_ipc_list))
		172	schedule_work(&free_ipc_work);
153	}	173	}
154	}	174	}
155		175