linux-kernel - [PATCH 3/3] tty: hvc: hvc_write() fix break condition

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Date:   Wed,  5 Sep 2018 22:14:39 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Nicholas Piggin <npiggin@...il.com>, Jiri Slaby <jslaby@...e.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Matteo Croce <mcroce@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org (op)
Subject: [PATCH 3/3] tty: hvc: hvc_write() fix break condition

Commit 550ddadcc758 ("tty: hvc: hvc_write() may sleep") broke the
termination condition in case the driver stops accepting characters.
This can result in unnecessary polling of the busy driver.

Restore it by testing the hvc_push return code.

Fixes: 550ddadcc758 ("tty: hvc: hvc_write() may sleep")
Tested-by: Matteo Croce <mcroce@...hat.com>
Tested-by: Leon Romanovsky <leonro@...lanox.com>
Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
 drivers/tty/hvc/hvc_console.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index bacf9b73ec98..c09a38fb0d66 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -522,6 +522,8 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
 		return -EIO;
 
 	while (count > 0) {
+		int ret;
+
 		spin_lock_irqsave(&hp->lock, flags);
 
 		rsize = hp->outbuf_size - hp->n_outbuf;
@@ -537,10 +539,13 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
 		}
 
 		if (hp->n_outbuf > 0)
-			hvc_push(hp);
+			ret = hvc_push(hp);
 
 		spin_unlock_irqrestore(&hp->lock, flags);
 
+		if (!ret)
+			break;
+
 		if (count) {
 			if (hp->n_outbuf > 0)
 				hvc_flush(hp);
-- 
2.18.0