[PATCH] knfsd: test and set SK_BUSY atomically
The SK_BUSY bit in svc_sock->sk_flags ensures that we do not attempt to
enqueue a socket twice. Currently, setting and clearing the bit is protected
by svc_serv->sv_lock. As I intend to reduce the data that the lock protects
so it's not held when svc_sock_enqueue() tests and sets SK_BUSY, that test and
set needs to be atomic.
Signed-off-by: Greg Banks <gnb@melbourne.sgi.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 88b51c4..a38df45 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -46,14 +46,13 @@
/* SMP locking strategy:
*
- * svc_serv->sv_lock protects most stuff for that service.
+ * svc_serv->sv_lock protects most stuff for that service.
* svc_sock->sk_defer_lock protects the svc_sock->sk_deferred list
+ * svc_sock->sk_flags.SK_BUSY prevents a svc_sock being enqueued multiply.
*
* Some flags can be set to certain values at any time
* providing that certain rules are followed:
*
- * SK_BUSY can be set to 0 at any time.
- * svc_sock_enqueue must be called afterwards
* SK_CONN, SK_DATA, can be set or cleared at any time.
* after a set, svc_sock_enqueue must be called.
* after a clear, the socket must be read/accepted
@@ -170,8 +169,13 @@
goto out_unlock;
}
- if (test_bit(SK_BUSY, &svsk->sk_flags)) {
- /* Don't enqueue socket while daemon is receiving */
+ /* Mark socket as busy. It will remain in this state until the
+ * server has processed all pending data and put the socket back
+ * on the idle list. We update SK_BUSY atomically because
+ * it also guards against trying to enqueue the svc_sock twice.
+ */
+ if (test_and_set_bit(SK_BUSY, &svsk->sk_flags)) {
+ /* Don't enqueue socket while already enqueued */
dprintk("svc: socket %p busy, not enqueued\n", svsk->sk_sk);
goto out_unlock;
}
@@ -185,15 +189,11 @@
dprintk("svc: socket %p no space, %d*2 > %ld, not enqueued\n",
svsk->sk_sk, atomic_read(&svsk->sk_reserved)+serv->sv_bufsz,
svc_sock_wspace(svsk));
+ clear_bit(SK_BUSY, &svsk->sk_flags);
goto out_unlock;
}
clear_bit(SOCK_NOSPACE, &svsk->sk_sock->flags);
- /* Mark socket as busy. It will remain in this state until the
- * server has processed all pending data and put the socket back
- * on the idle list.
- */
- set_bit(SK_BUSY, &svsk->sk_flags);
if (!list_empty(&serv->sv_threads)) {
rqstp = list_entry(serv->sv_threads.next,