Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL

The poll() changes were not well thought out, and completely
unexplained.  They also caused a huge performance regression, because
"->poll()" was no longer a trivial file operation that just called down
to the underlying file operations, but instead did at least two indirect
calls.

Indirect calls are sadly slow now with the Spectre mitigation, but the
performance problem could at least be largely mitigated by changing the
"->get_poll_head()" operation to just have a per-file-descriptor pointer
to the poll head instead.  That gets rid of one of the new indirections.

But that doesn't fix the new complexity that is completely unwarranted
for the regular case.  The (undocumented) reason for the poll() changes
was some alleged AIO poll race fixing, but we don't make the common case
slower and more complex for some uncommon special case, so this all
really needs way more explanations and most likely a fundamental
redesign.

[ This revert is a revert of about 30 different commits, not reverted
  individually because that would just be unnecessarily messy  - Linus ]

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 11 insertions, 6 deletions

diff --git a/net/atm/common.c b/net/atm/common.c
index ff5748b2190f..a7a68e509628 100644
--- a/net/atm/common.c
+++ b/net/atm/common.c
@@ -647,11 +647,16 @@ out:
 	return error;
 }
 
-__poll_t vcc_poll_mask(struct socket *sock, __poll_t events)
+__poll_t vcc_poll(struct file *file, struct socket *sock, poll_table *wait)
 {
 	struct sock *sk = sock->sk;
-	struct atm_vcc *vcc = ATM_SD(sock);
-	__poll_t mask = 0;
+	struct atm_vcc *vcc;
+	__poll_t mask;
+
+	sock_poll_wait(file, sk_sleep(sk), wait);
+	mask = 0;
+
+	vcc = ATM_SD(sock);
 
 	/* exceptional events */
 	if (sk->sk_err)
diff --git a/net/atm/common.h b/net/atm/common.h
index 526796ad230f..5850649068bb 100644
--- a/net/atm/common.h
+++ b/net/atm/common.h
@@ -17,7 +17,7 @@ int vcc_connect(struct socket *sock, int itf, short vpi, int vci);
 int vcc_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 		int flags);
 int vcc_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len);
-__poll_t vcc_poll_mask(struct socket *sock, __poll_t events);
+__poll_t vcc_poll(struct file *file, struct socket *sock, poll_table *wait);
 int vcc_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
 int vcc_compat_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
 int vcc_setsockopt(struct socket *sock, int level, int optname,
diff --git a/net/atm/pvc.c b/net/atm/pvc.c
index 9f75092fe778..2cb10af16afc 100644
--- a/net/atm/pvc.c
+++ b/net/atm/pvc.c
@@ -113,7 +113,7 @@ static const struct proto_ops pvc_proto_ops = {
 	.socketpair =	sock_no_socketpair,
 	.accept =	sock_no_accept,
 	.getname =	pvc_getname,
-	.poll_mask =	vcc_poll_mask,
+	.poll =		vcc_poll,
 	.ioctl =	vcc_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl = vcc_compat_ioctl,
diff --git a/net/atm/svc.c b/net/atm/svc.c
index 53f4ad7087b1..2f91b766ac42 100644
--- a/net/atm/svc.c
+++ b/net/atm/svc.c
@@ -636,7 +636,7 @@ static const struct proto_ops svc_proto_ops = {
 	.socketpair =	sock_no_socketpair,
 	.accept =	svc_accept,
 	.getname =	svc_getname,
-	.poll_mask =	vcc_poll_mask,
+	.poll =		vcc_poll,
 	.ioctl =	svc_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl =	svc_compat_ioctl,