From: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
On exiting of the last task in a namespace we need to trigger freeing of
the namespace. Currently, we call synchronize_rcu() and free_nsproxy()
directly on do_exit() path.
On my machine synchronize_rcu() blocks for about 0.01 seconds. For
comparing: normal exit_group() syscall takes less than 0.0003 seconds.
Let's offload synchronize_rcu() and free_nsproxy() to a workqueue.
I also move synchronize_rcu() inside free_nsproxy(). It fixes racy
put_nsproxy() which calls free_nsproxy() without synchronize_rcu().
I guess it was missed during switch to RCU (see cf7b708).
Microbenchmark:
: #define _GNU_SOURCE
: #include <unistd.h>
: #include <sched.h>
: #include <stdlib.h>
: #include <sys/wait.h>
:
: int
: main(void)
: {
: int i;
: for (i = 0; i < 1024; i++) {
: if (fork()) {
: wait(NULL);
: continue;
: }
: unshare(CLONE_NEWIPC);
: exit(0);
: }
: return 0;
: }
Before the patch:
real 0m8.335s
user 0m0.000s
sys 0m0.265s
After:
real 0m0.569s
user 0m0.001s
sys 0m0.154s
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Acked-by: Serge E. Hallyn <serge.hal...@ubuntu.com>
---
v2:
- Updated description.
---
include/linux/nsproxy.h | 1 +
kernel/nsproxy.c | 34 +++++++++++++++++++++++-----------
2 files changed, 24 insertions(+), 11 deletions(-)
diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index cc37a55..1d26be7 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -24,6 +24,7 @@ struct fs_struct;
*/
struct nsproxy {
atomic_t count;
+ struct work_struct free_nsproxy_work;
struct uts_namespace *uts_ns;
struct ipc_namespace *ipc_ns;
struct mnt_namespace *mnt_ns;
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index b576f7f..ebc7d40 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -41,13 +41,17 @@ struct nsproxy init_nsproxy = {
#endif
};
+static void free_nsproxy_work(struct work_struct *work);
+
static inline struct nsproxy *create_nsproxy(void)
{
struct nsproxy *nsproxy;
nsproxy = kmem_cache_alloc(nsproxy_cachep, GFP_KERNEL);
- if (nsproxy)
+ if (nsproxy) {
atomic_set(&nsproxy->count, 1);
+ INIT_WORK(&nsproxy->free_nsproxy_work, free_nsproxy_work);
+ }
return nsproxy;
}
@@ -166,6 +170,14 @@ out:
void free_nsproxy(struct nsproxy *ns)
{
+ /*
+ * wait for others to get what they want from this nsproxy.
+ *
+ * cannot release this nsproxy via the call_rcu() since
+ * put_mnt_ns() will want to sleep
+ */
+ synchronize_rcu();
+
if (ns->mnt_ns)
put_mnt_ns(ns->mnt_ns);
if (ns->uts_ns)
@@ -178,6 +190,14 @@ void free_nsproxy(struct nsproxy *ns)
kmem_cache_free(nsproxy_cachep, ns);
}
+static void free_nsproxy_work(struct work_struct *work)
+{
+ struct nsproxy *ns = container_of(work, struct nsproxy,
+ free_nsproxy_work);
+
+ free_nsproxy(ns);
+}
+
/*
* Called from unshare. Unshare all the namespaces part of nsproxy.
* On success, returns the new nsproxy.
@@ -215,16 +235,8 @@ void switch_task_namespaces(struct task_struct *p, struct
nsproxy *new)
rcu_assign_pointer(p->nsproxy, new);
- if (ns && atomic_dec_and_test(&ns->count)) {
- /*
- * wait for others to get what they want from this nsproxy.
- *
- * cannot release this nsproxy via the call_rcu() since
- * put_mnt_ns() will want to sleep
- */
- synchronize_rcu();
- free_nsproxy(ns);
- }
+ if (ns && atomic_dec_and_test(&ns->count))
+ schedule_work(&ns->free_nsproxy_work);
}
void exit_task_namespaces(struct task_struct *p)
--
1.7.7.6
--
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