From: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
Subject: 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");
}
gets 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
Link: http://lkml.kernel.org/r/20200225145419.527994-1-gscrivan@xxxxxxxxxx
Signed-off-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/ipc_namespace.h | 2 ++
ipc/namespace.c | 24 ++++++++++++++++++++++--
2 files changed, 24 insertions(+), 2 deletions(-)
--- a/include/linux/ipc_namespace.h~ipc-use-a-work-queue-to-free_ipc
+++ a/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;
--- a/ipc/namespace.c~ipc-use-a-work-queue-to-free_ipc
+++ a/ipc/namespace.c
@@ -117,6 +117,10 @@ void free_ipcs(struct ipc_namespace *ns,
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_names
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);
}
}
_
