[PATCH] knfsd: fix a race in closing NFSd connections
If you lose this race, it can iput a socket inode twice and you get a BUG
in fs/inode.c
When I added the option for user-space to close a socket, I added some
cruft to svc_delete_socket so that I could call that function when closing
a socket per user-space request.
This was the wrong thing to do. I should have just set SK_CLOSE and let
normal mechanisms do the work.
Not only wrong, but buggy. The locking is all wrong and it openned up a
race where-by a socket could be closed twice.
So this patch:
Introduces svc_close_socket which sets SK_CLOSE then either leave
the close up to a thread, or calls svc_delete_socket if it can
get SK_BUSY.
Adds a bias to sk_busy which is removed when SK_DEAD is set,
This avoid races around shutting down the socket.
Changes several 'spin_lock' to 'spin_lock_bh' where the _bh
was missing.
Bugzilla-url: http://bugzilla.kernel.org/show_bug.cgi?id=7916
Signed-off-by: Neil Brown <neilb@suse.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index ff1f8bf..cf93cd1 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -62,6 +62,12 @@
* after a clear, the socket must be read/accepted
* if this succeeds, it must be set again.
* SK_CLOSE can set at any time. It is never cleared.
+ * sk_inuse contains a bias of '1' until SK_DEAD is set.
+ * so when sk_inuse hits zero, we know the socket is dead
+ * and no-one is using it.
+ * SK_DEAD can only be set while SK_BUSY is held which ensures
+ * no other thread will be using the socket or will try to
+ * set SK_DEAD.
*
*/
@@ -70,6 +76,7 @@
static struct svc_sock *svc_setup_socket(struct svc_serv *, struct socket *,
int *errp, int pmap_reg);
+static void svc_delete_socket(struct svc_sock *svsk);
static void svc_udp_data_ready(struct sock *, int);
static int svc_udp_recvfrom(struct svc_rqst *);
static int svc_udp_sendto(struct svc_rqst *);
@@ -329,8 +336,9 @@
static inline void
svc_sock_put(struct svc_sock *svsk)
{
- if (atomic_dec_and_test(&svsk->sk_inuse) &&
- test_bit(SK_DEAD, &svsk->sk_flags)) {
+ if (atomic_dec_and_test(&svsk->sk_inuse)) {
+ BUG_ON(! test_bit(SK_DEAD, &svsk->sk_flags));
+
dprintk("svc: releasing dead socket\n");
if (svsk->sk_sock->file)
sockfd_put(svsk->sk_sock);
@@ -520,7 +528,7 @@
if (!serv)
return 0;
- spin_lock(&serv->sv_lock);
+ spin_lock_bh(&serv->sv_lock);
list_for_each_entry(svsk, &serv->sv_permsocks, sk_list) {
int onelen = one_sock_name(buf+len, svsk);
if (toclose && strcmp(toclose, buf+len) == 0)
@@ -528,12 +536,12 @@
else
len += onelen;
}
- spin_unlock(&serv->sv_lock);
+ spin_unlock_bh(&serv->sv_lock);
if (closesk)
/* Should unregister with portmap, but you cannot
* unregister just one protocol...
*/
- svc_delete_socket(closesk);
+ svc_close_socket(closesk);
else if (toclose)
return -ENOENT;
return len;
@@ -683,6 +691,11 @@
return svc_deferred_recv(rqstp);
}
+ if (test_bit(SK_CLOSE, &svsk->sk_flags)) {
+ svc_delete_socket(svsk);
+ return 0;
+ }
+
clear_bit(SK_DATA, &svsk->sk_flags);
while ((skb = skb_recv_datagram(svsk->sk_sk, 0, 1, &err)) == NULL) {
if (err == -EAGAIN) {
@@ -1176,7 +1189,8 @@
rqstp->rq_sock->sk_server->sv_name,
(sent<0)?"got error":"sent only",
sent, xbufp->len);
- svc_delete_socket(rqstp->rq_sock);
+ set_bit(SK_CLOSE, &rqstp->rq_sock->sk_flags);
+ svc_sock_enqueue(rqstp->rq_sock);
sent = -EAGAIN;
}
return sent;
@@ -1495,7 +1509,7 @@
svsk->sk_odata = inet->sk_data_ready;
svsk->sk_owspace = inet->sk_write_space;
svsk->sk_server = serv;
- atomic_set(&svsk->sk_inuse, 0);
+ atomic_set(&svsk->sk_inuse, 1);
svsk->sk_lastrecv = get_seconds();
spin_lock_init(&svsk->sk_defer_lock);
INIT_LIST_HEAD(&svsk->sk_deferred);
@@ -1618,7 +1632,7 @@
/*
* Remove a dead socket
*/
-void
+static void
svc_delete_socket(struct svc_sock *svsk)
{
struct svc_serv *serv;
@@ -1644,16 +1658,26 @@
* while still attached to a queue, the queue itself
* is about to be destroyed (in svc_destroy).
*/
- if (!test_and_set_bit(SK_DEAD, &svsk->sk_flags))
+ if (!test_and_set_bit(SK_DEAD, &svsk->sk_flags)) {
+ BUG_ON(atomic_read(&svsk->sk_inuse)<2);
+ atomic_dec(&svsk->sk_inuse);
if (test_bit(SK_TEMP, &svsk->sk_flags))
serv->sv_tmpcnt--;
+ }
- /* This atomic_inc should be needed - svc_delete_socket
- * should have the semantic of dropping a reference.
- * But it doesn't yet....
- */
- atomic_inc(&svsk->sk_inuse);
spin_unlock_bh(&serv->sv_lock);
+}
+
+void svc_close_socket(struct svc_sock *svsk)
+{
+ set_bit(SK_CLOSE, &svsk->sk_flags);
+ if (test_and_set_bit(SK_BUSY, &svsk->sk_flags))
+ /* someone else will have to effect the close */
+ return;
+
+ atomic_inc(&svsk->sk_inuse);
+ svc_delete_socket(svsk);
+ clear_bit(SK_BUSY, &svsk->sk_flags);
svc_sock_put(svsk);
}