linux-kernel - [PATCH 4.4 03/76] HID: hidraw, uhid: Always report EPOLLOUT

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Date:   Wed, 22 Jan 2020 10:28:19 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 03/76] HID: hidraw, uhid: Always report EPOLLOUT

From: Jiri Kosina <jkosina@...e.cz>

[ Upstream commit 9e635c2851df6caee651e589fbf937b637973c91 ]

hidraw and uhid device nodes are always available for writing so we should
always report EPOLLOUT and EPOLLWRNORM bits, not only in the cases when
there is nothing to read.

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Fixes: be54e7461ffdc ("HID: uhid: Fix returning EPOLLOUT from uhid_char_poll")
Fixes: 9f3b61dc1dd7b ("HID: hidraw: Fix returning EPOLLOUT from hidraw_poll")
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/hid/hidraw.c | 7 ++++---
 drivers/hid/uhid.c   | 5 +++--
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index e60d9c88bd35..ef9e196b54a5 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -262,13 +262,14 @@ out:
 static unsigned int hidraw_poll(struct file *file, poll_table *wait)
 {
 	struct hidraw_list *list = file->private_data;
+	unsigned int mask = POLLOUT | POLLWRNORM; /* hidraw is always writable */
 
 	poll_wait(file, &list->hidraw->wait, wait);
 	if (list->head != list->tail)
-		return POLLIN | POLLRDNORM;
+		mask |= POLLIN | POLLRDNORM;
 	if (!list->hidraw->exist)
-		return POLLERR | POLLHUP;
-	return POLLOUT | POLLWRNORM;
+		mask |= POLLERR | POLLHUP;
+	return mask;
 }
 
 static int hidraw_open(struct inode *inode, struct file *file)
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index ea0c860ee842..a7ba4db8cff7 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -769,13 +769,14 @@ unlock:
 static unsigned int uhid_char_poll(struct file *file, poll_table *wait)
 {
 	struct uhid_device *uhid = file->private_data;
+	unsigned int mask = POLLOUT | POLLWRNORM; /* uhid is always writable */
 
 	poll_wait(file, &uhid->waitq, wait);
 
 	if (uhid->head != uhid->tail)
-		return POLLIN | POLLRDNORM;
+		mask |= POLLIN | POLLRDNORM;
 
-	return EPOLLOUT | EPOLLWRNORM;
+	return mask;
 }
 
 static const struct file_operations uhid_fops = {
-- 
2.20.1