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authorGiuseppe Scrivano <gscrivan@redhat.com>2020-06-08 07:40:10 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-08 21:05:56 +0300
commite1eb26fa62d04ec0955432be1aa8722a97cb52e7 (patch)
tree7321dbd441a768088a9c8e397ae540f1e9a26c1f
parent4b78e2013a374f379457ceba7dc860d9fc28156b (diff)
downloadlinux-e1eb26fa62d04ec0955432be1aa8722a97cb52e7.tar.xz
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 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>
-rw-r--r--include/linux/ipc_namespace.h2
-rw-r--r--ipc/namespace.c24
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);
}
}