linux-kernel - [PATCH 4.2.y-ckt 102/218] xtensa: ISS: don't hang if stdin EOF is reached

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Message-Id: <1459455431-12687-103-git-send-email-kamal@canonical.com>
Date:	Thu, 31 Mar 2016 13:15:15 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Max Filippov <jcmvbkbc@...il.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 102/218] xtensa: ISS: don't hang if stdin EOF is reached

4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

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

From: Max Filippov <jcmvbkbc@...il.com>

commit 362014c8d9d51d504c167c44ac280169457732be upstream.

Simulator stdin may be connected to a file, when its end is reached
kernel hangs in infinite loop inside rs_poll, because simc_poll always
signals that descriptor 0 is readable and simc_read always returns 0.
Check simc_read return value and exit loop if it's not positive. Also
don't rewind polling timer if it's zero.

Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/xtensa/platforms/iss/console.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/xtensa/platforms/iss/console.c b/arch/xtensa/platforms/iss/console.c
index 70cb408..92d785f 100644
--- a/arch/xtensa/platforms/iss/console.c
+++ b/arch/xtensa/platforms/iss/console.c
@@ -100,21 +100,23 @@ static void rs_poll(unsigned long priv)
 {
 	struct tty_port *port = (struct tty_port *)priv;
 	int i = 0;
+	int rd = 1;
 	unsigned char c;
 
 	spin_lock(&timer_lock);
 
 	while (simc_poll(0)) {
-		simc_read(0, &c, 1);
+		rd = simc_read(0, &c, 1);
+		if (rd <= 0)
+			break;
 		tty_insert_flip_char(port, c, TTY_NORMAL);
 		i++;
 	}
 
 	if (i)
 		tty_flip_buffer_push(port);
-
-
-	mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE);
+	if (rd)
+		mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE);
 	spin_unlock(&timer_lock);
 }
 
-- 
2.7.4