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[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>
This commit is contained in:
NeilBrown 2007-02-08 14:20:30 -08:00 committed by Linus Torvalds
parent 387bb17374
commit aaf68cfbf2
3 changed files with 41 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/sunrpc/svcsock.h
View File

@ -63,7 +63,7 @@ struct svc_sock {
* Function prototypes.
*/
int svc_makesock(struct svc_serv *, int, unsigned short);
void svc_delete_socket(struct svc_sock *);
void svc_close_socket(struct svc_sock *);
int svc_recv(struct svc_rqst *, long);
int svc_send(struct svc_rqst *);
void svc_drop(struct svc_rqst *);

4
net/sunrpc/svc.c
View File

@ -386,7 +386,7 @@ svc_destroy(struct svc_serv *serv)
svsk = list_entry(serv->sv_tempsocks.next,
struct svc_sock,
sk_list);
svc_delete_socket(svsk);
svc_close_socket(svsk);
}
if (serv->sv_shutdown)
serv->sv_shutdown(serv);
@ -395,7 +395,7 @@ svc_destroy(struct svc_serv *serv)
svsk = list_entry(serv->sv_permsocks.next,
struct svc_sock,
sk_list);
svc_delete_socket(svsk);
svc_close_socket(svsk);
}
cache_clean_deferred(serv);

52
net/sunrpc/svcsock.c
View File

@ -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 @@ void svc_reserve(struct svc_rqst *rqstp, int space)
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 @@ svc_sock_names(char *buf, struct svc_serv *serv, char *toclose)
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 @@ svc_sock_names(char *buf, struct svc_serv *serv, char *toclose)
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 @@ svc_udp_recvfrom(struct svc_rqst *rqstp)
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 @@ svc_tcp_sendto(struct svc_rqst *rqstp)
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 @@ svc_setup_socket(struct svc_serv *serv, struct socket *sock,
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 @@ bummer:
/*
* Remove a dead socket
*/
void
static void
svc_delete_socket(struct svc_sock *svsk)
{
struct svc_serv *serv;
@ -1644,16 +1658,26 @@ svc_delete_socket(struct svc_sock *svsk)
* 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);
}