From e1eb26fa62d04ec0955432be1aa8722a97cb52e7 Mon Sep 17 00:00:00 2001 From: Giuseppe Scrivano Date: Sun, 7 Jun 2020 21:40:10 -0700 Subject: [PATCH] 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 #include #include #include 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 Signed-off-by: Andrew Morton Reviewed-by: Paul E. McKenney Reviewed-by: Waiman Long Cc: Davidlohr Bueso Cc: Manfred Spraul Link: http://lkml.kernel.org/r/20200225145419.527994-1-gscrivan@redhat.com Signed-off-by: Linus Torvalds --- include/linux/ipc_namespace.h | 2 ++ ipc/namespace.c | 24 ++++++++++++++++++++++-- 2 files changed, 24 insertions(+), 2 deletions(-) diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index c309f43bde45..a06a78c67f19 100644 --- a/include/linux/ipc_namespace.h +++ b/include/linux/ipc_namespace.h @@ -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; diff --git a/ipc/namespace.c b/ipc/namespace.c index fdc3b5f3f53a..24e7b45320f7 100644 --- a/ipc/namespace.c +++ b/ipc/namespace.c @@ -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); } }