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From: Nicholas Piggin <npiggin@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>, Jiri Slaby <jslaby@suse.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Matteo Croce <mcroce@redhat.com>,
	Jason Gunthorpe <jgg@mellanox.com>,
	Leon Romanovsky <leonro@mellanox.com>,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org (op)
Subject: [PATCH v2 3/3] tty: hvc: hvc_write() fix break condition
Date: Sun,  9 Sep 2018 15:39:16 +1000	[thread overview]
Message-ID: <20180909053916.14139-4-npiggin@gmail.com> (raw)
In-Reply-To: <20180909053916.14139-1-npiggin@gmail.com>

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.

Tested-by: Matteo Croce <mcroce@redhat.com>
Tested-by: Jason Gunthorpe <jgg@mellanox.com>
Tested-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.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..27284a2dcd2b 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 = 0;
+
 		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


  parent reply	other threads:[~2018-09-09  5:39 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-09  5:39 [PATCH v2 0/3] tty: hvc: latency break regression fixes Nicholas Piggin
2018-09-09  5:39 ` [PATCH v2 1/3] tty: hvc: hvc_poll() fix read loop hang Nicholas Piggin
2018-09-09  5:39 ` [PATCH v2 2/3] tty: hvc: hvc_poll() fix read loop batching Nicholas Piggin
2018-09-09  5:39 ` Nicholas Piggin [this message]
2018-09-10 16:04 ` [PATCH v2 0/3] tty: hvc: latency break regression fixes Greg Kroah-Hartman

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