IB/umad: Return EPOLLERR in case of when device disassociated

Currently, polling a umad device will always works, even if the device was
disassociated. A disassociated device should immediately return EPOLLERR
from poll(). Otherwise userspace is endlessly hung on poll() with no idea
that the device has been removed from the system.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/r/20210125121339.837518-3-leon@kernel.orgSigned-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/user_mad.c

@@ -397,6 +397,11 @@ static ssize_t ib_umad_read(struct file *filp, char __user *buf,
 		mutex_lock(&file->mutex);
 	}
 
+	if (file->agents_dead) {
+		mutex_unlock(&file->mutex);
+		return -EIO;
+	}
+
 	packet = list_entry(file->recv_list.next, struct ib_umad_packet, list);
 	list_del(&packet->list);
 
@@ -658,10 +663,14 @@ static __poll_t ib_umad_poll(struct file *filp, struct poll_table_struct *wait)
 	/* we will always be able to post a MAD send */
 	__poll_t mask = EPOLLOUT | EPOLLWRNORM;
 
+	mutex_lock(&file->mutex);
 	poll_wait(filp, &file->recv_wait, wait);
 
 	if (!list_empty(&file->recv_list))
 		mask |= EPOLLIN | EPOLLRDNORM;
+	if (file->agents_dead)
+		mask = EPOLLERR;
+	mutex_unlock(&file->mutex);
 
 	return mask;
 }
@@ -1341,6 +1350,7 @@ static void ib_umad_kill_port(struct ib_umad_port *port)
 	list_for_each_entry(file, &port->file_list, port_list) {
 		mutex_lock(&file->mutex);
 		file->agents_dead = 1;
+		wake_up_interruptible(&file->recv_wait);
 		mutex_unlock(&file->mutex);
 
 		for (id = 0; id < IB_UMAD_MAX_AGENTS; ++id)