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From:   Zhaolong Zhang <zhangzl2013@126.com>
To:     gregkh@linuxfoundation.org
Cc:     linux-kernel@vger.kernel.org, xiubli@redhat.com,
        ying.xue@windriver.com, hamish.martin@alliedtelesis.co.nz
Subject: [PATCH] uio: dismiss waiters on device unregistration
Date:   Fri, 16 Nov 2018 18:21:51 +0800
Message-Id: <1542363711-23231-1-git-send-email-zhangzl2013@126.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

When the device is unregistered, it should wake up the blocking waiters.
Otherwise, they will sleep forever.

Signed-off-by: Zhaolong Zhang <zhangzl2013@126.com>
---
 drivers/uio/uio.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 8564466..08fa55d 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -569,20 +569,20 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
 	ssize_t retval = 0;
 	s32 event_count;
 
-	mutex_lock(&idev->info_lock);
-	if (!idev->info || !idev->info->irq)
-		retval = -EIO;
-	mutex_unlock(&idev->info_lock);
-
-	if (retval)
-		return retval;
-
 	if (count != sizeof(s32))
 		return -EINVAL;
 
 	add_wait_queue(&idev->wait, &wait);
 
 	do {
+		mutex_lock(&idev->info_lock);
+		if (!idev->info || !idev->info->irq) {
+			retval = -EIO;
+			mutex_unlock(&idev->info_lock);
+			break;
+		}
+		mutex_unlock(&idev->info_lock);
+
 		set_current_state(TASK_INTERRUPTIBLE);
 
 		event_count = atomic_read(&idev->event);
@@ -1014,6 +1014,9 @@ void uio_unregister_device(struct uio_info *info)
 	idev->info = NULL;
 	mutex_unlock(&idev->info_lock);
 
+	wake_up_interruptible(&idev->wait);
+	kill_fasync(&idev->async_queue, SIGIO, POLL_HUP);
+
 	device_unregister(&idev->dev);
 
 	return;
-- 
1.9.1