lkml.org 
[lkml]   [2017]   [Oct]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC][PATCH 6/8] epoll: ensure the validity of ep when removing epi in eventpoll_release_file()
Date
Before the removal of epmutex, ep_free() will be blocked by epmutex when
invoking eventpoll_release_file(), so epi->ep will be valid.

After the removal of epmutex, epi->ep may be freed during the invocation
of eventpoll_release_file(). We can not use rcu_read_lock/unlock because
we needs to acquire ep->mtx which is a mutex, so we add a ref-counter to
eventpoll and increase it before leaving the rcu read critical region.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
fs/eventpoll.c | 38 +++++++++++++++++++++++++++++++-------
1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index e1e4796..27b743b 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -43,6 +43,7 @@
#include <linux/compat.h>
#include <linux/rculist.h>
#include <net/busy_poll.h>
+#include <linux/refcount.h>

/*
* LOCKING:
@@ -231,6 +232,8 @@ struct eventpoll {
unsigned int napi_id;
#endif

+ /* used to ensure the validity of eventpoll when release file */
+ refcount_t ref;
/* used to free itself */
struct rcu_head rcu;
};
@@ -827,6 +830,25 @@ static void ep_rcu_free(struct rcu_head *head)
kfree(ep);
}

+static void eventpoll_put_ep(struct eventpoll *ep)
+{
+ if (refcount_dec_and_test(&ep->ref)) {
+ mutex_destroy(&ep->mtx);
+ free_uid(ep->user);
+ wakeup_source_unregister(ep->ws);
+
+ call_rcu(&ep->rcu, ep_rcu_free);
+ }
+}
+
+static struct eventpoll *eventpoll_get_ep(struct eventpoll *ep)
+{
+ if (refcount_inc_not_zero(&ep->ref))
+ return ep;
+ else
+ return NULL;
+}
+
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
@@ -883,11 +905,7 @@ static void ep_free(struct eventpoll *ep)
mutex_unlock(&epmutex);
}

- mutex_destroy(&ep->mtx);
- free_uid(ep->user);
- wakeup_source_unregister(ep->ws);
-
- call_rcu(&ep->rcu, ep_rcu_free);
+ eventpoll_put_ep(ep);
}

static int ep_eventpoll_release(struct inode *inode, struct file *file)
@@ -1018,7 +1036,7 @@ static const struct file_operations eventpoll_fops = {
void eventpoll_release_file(struct file *file)
{
struct eventpoll *ep;
- struct epitem *epi, *next;
+ struct epitem *epi;

/*
* We don't want to get "file->f_lock" because it is not
@@ -1039,13 +1057,18 @@ void eventpoll_release_file(struct file *file)
if (!epi)
break;

- ep = epi->ep;
+ ep = eventpoll_get_ep(epi->ep);
+ /* Current epi has been removed by ep_free() */
+ if (!ep)
+ continue;
rcu_read_unlock();

mutex_lock_nested(&ep->mtx, 0);
ep_remove(ep, epi);
mutex_unlock(&ep->mtx);

+ eventpoll_put_ep(ep);
+
rcu_read_lock();
}
rcu_read_unlock();
@@ -1084,6 +1107,7 @@ static int ep_alloc(struct eventpoll **pep)
ep->ovflist = EP_UNACTIVE_PTR;
ep->user = user;
INIT_LIST_HEAD(&ep->visited_list_link);
+ refcount_set(&ep->ref, 1);

*pep = ep;

--
2.7.5
\
 
 \ /
  Last update: 2017-10-28 20:22    [W:0.064 / U:2.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site