From: Li RongQing <lirongqing@baidu.com>
To: gregkh@linuxfoundation.org, jslaby@suse.com,
linux-kernel@vger.kernel.org, gkohli@codeaurora.org
Subject: [PATCH][v4] tty: fix race between flush_to_ldisc and tty_open
Date: Fri, 18 Jan 2019 17:27:17 +0800 [thread overview]
Message-ID: <1547803637-29135-1-git-send-email-lirongqing@baidu.com> (raw)
There still is a race window after the commit b027e2298bd588
("tty: fix data race between tty_init_dev and flush of buf"),
and we encountered this crash issue if receive_buf call comes
before tty initialization completes in n_tty_open and
tty->driver_data may be NULL.
CPU0 CPU1
---- ----
n_tty_open
tty_init_dev
tty_ldisc_unlock
schedule
flush_to_ldisc
receive_buf
tty_port_default_receive_buf
tty_ldisc_receive_buf
n_tty_receive_buf_common
__receive_buf
uart_flush_chars
uart_start
/*tty->driver_data is NULL*/
tty->ops->open
/*init tty->driver_data*/
it can be fixed by extending ldisc semaphore lock in tty_init_dev
to driver_data initialized completely after tty->ops->open(), but
this will lead to put lock on one function and unlock in some other
function, and hard to maintain, so fix this race only by checking
tty->driver_data when receiving, and return if tty->driver_data
is NULL
Signed-off-by: Wang Li <wangli39@baidu.com>
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
V4: add version information
V3: not used ldisc semaphore lock, only checking tty->driver_data with NULL
V2: fix building error by EXPORT_SYMBOL tty_ldisc_unlock
V1: extend ldisc lock to protect that tty->driver_data is inited
drivers/tty/tty_port.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 044c3cbdcfa4..86d0bec38322 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -31,6 +31,9 @@ static int tty_port_default_receive_buf(struct tty_port *port,
if (!tty)
return 0;
+ if (!tty->driver_data)
+ return 0;
+
disc = tty_ldisc_ref(tty);
if (!disc)
return 0;
--
2.16.2
next reply other threads:[~2019-01-18 9:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-18 9:27 Li RongQing [this message]
2019-01-18 12:50 ` [PATCH][v4] tty: fix race between flush_to_ldisc and tty_open Kohli, Gaurav
2019-01-30 9:29 ` 答复: " Li,Rongqing
2019-01-30 10:19 ` Greg KH
2019-01-30 12:48 ` 答复: " Li,Rongqing
2019-01-30 13:16 ` Greg KH
2019-01-31 2:15 ` 答复: " Li,Rongqing
2019-01-31 6:52 ` Greg KH
2019-01-31 7:40 ` 答复: " Li,Rongqing
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1547803637-29135-1-git-send-email-lirongqing@baidu.com \
--to=lirongqing@baidu.com \
--cc=gkohli@codeaurora.org \
--cc=gregkh@linuxfoundation.org \
--cc=jslaby@suse.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).