linux-kernel - [PATCH 3.16.y-ckt 053/180] posix-clock: Fix return code on the poll method's error path

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Message-Id: <1454538786-12215-54-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  3 Feb 2016 22:30:59 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	John Stultz <john.stultz@...aro.org>,
	Julia Lawall <julia.lawall@...6.fr>,
	Thomas Gleixner <tglx@...utronix.de>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 053/180] posix-clock: Fix return code on the poll method's error path

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Richard Cochran <richardcochran@...il.com>

commit 1b9f23727abb92c5e58f139e7d180befcaa06fe0 upstream.

The posix_clock_poll function is supposed to return a bit mask of
POLLxxx values.  However, in case the hardware has disappeared (due to
hot plugging for example) this code returns -ENODEV in a futile
attempt to throw an error at the file descriptor level.  The kernel's
file_operations interface does not accept such error codes from the
poll method.  Instead, this function aught to return POLLERR.

The value -ENODEV does, in fact, contain the POLLERR bit (and almost
all the other POLLxxx bits as well), but only by chance.  This patch
fixes code to return a proper bit mask.

Credit goes to Markus Elfring for pointing out the suspicious
signed/unsigned mismatch.

Reported-by: Markus Elfring <elfring@...rs.sourceforge.net>
igned-off-by: Richard Cochran <richardcochran@...il.com>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Julia Lawall <julia.lawall@...6.fr>
Link: http://lkml.kernel.org/r/1450819198-17420-1-git-send-email-richardcochran@gmail.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 kernel/time/posix-clock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/posix-clock.c b/kernel/time/posix-clock.c
index ce033c7aa2e8..9cff0ab82b63 100644
--- a/kernel/time/posix-clock.c
+++ b/kernel/time/posix-clock.c
@@ -69,10 +69,10 @@ static ssize_t posix_clock_read(struct file *fp, char __user *buf,
 static unsigned int posix_clock_poll(struct file *fp, poll_table *wait)
 {
 	struct posix_clock *clk = get_posix_clock(fp);
-	int result = 0;
+	unsigned int result = 0;

 	if (!clk)
-		return -ENODEV;
+		return POLLERR;

 	if (clk->ops.poll)
 		result = clk->ops.poll(clk, fp, wait);