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

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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>
This commit is contained in:
Giuseppe Scrivano 2020-06-07 21:40:10 -07:00 committed by Linus Torvalds
parent 4b78e2013a
commit e1eb26fa62
2 changed files with 24 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/ipc_namespace.h
View File

@ -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;

24
ipc/namespace.c
View File

@ -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);
}
}