ipc/namespace.c: use a work queue to free_ipc (e1eb26fa) · Commits · 戴 / test

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 Signed-off-by:

Giuseppe Scrivano <gscrivan@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Reviewed-by:

Paul E. McKenney <paulmck@kernel.org> Reviewed-by:

Waiman Long <longman@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Manfred Spraul <manfred@colorfullife.com> Link: http://lkml.kernel.org/r/20200225145419.527994-1-gscrivan@redhat.com Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/ipc_namespace.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -68,6 +68,8 @@ struct ipc_namespace {
		struct user_namespace *user_ns;
		struct ucounts *ucounts;

		struct llist_node mnt_llist;

		struct ns_common ns;
		} __randomize_layout;

ipc/namespace.c

+22 −2

Original line number	Diff line number	Diff line
		@@ -117,6 +117,10 @@ void free_ipcs(struct ipc_namespace ns, struct ipc_ids ids,

		static void free_ipc_ns(struct ipc_namespace *ns)
		{
		/* mq_put_mnt() waits for a grace period as kern_unmount()
		* uses synchronize_rcu().
		*/
		mq_put_mnt(ns);
		sem_exit_ns(ns);
		msg_exit_ns(ns);
		shm_exit_ns(ns);
		@@ -127,6 +131,21 @@ static void free_ipc_ns(struct ipc_namespace *ns)
		kfree(ns);
		}

		static LLIST_HEAD(free_ipc_list);
		static void free_ipc(struct work_struct *unused)
		{
		struct llist_node *node = llist_del_all(&free_ipc_list);
		struct ipc_namespace n, t;

		llist_for_each_entry_safe(n, t, node, mnt_llist)
		free_ipc_ns(n);
		}

		/*
		* The work queue is used to avoid the cost of synchronize_rcu in kern_unmount.
		*/
		static DECLARE_WORK(free_ipc_work, free_ipc);

		/*
		* put_ipc_ns - drop a reference to an ipc namespace.
		* @ns: the namespace to put
		@@ -148,8 +167,9 @@ void put_ipc_ns(struct ipc_namespace *ns)
		if (refcount_dec_and_lock(&ns->count, &mq_lock)) {
		mq_clear_sbinfo(ns);
		spin_unlock(&mq_lock);
		mq_put_mnt(ns);
		free_ipc_ns(ns);

		if (llist_add(&ns->mnt_llist, &free_ipc_list))
		schedule_work(&free_ipc_work);
		}
		}

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