lkml.org 
[lkml]   [2021]   [Apr]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] ttyprintk: Add TTY hangup callback.
From
Date
On 18. 04. 21, 13:16, Samo Pogačnik wrote:
> Dne 15.04.2021 (čet) ob 09:22 +0900 je Tetsuo Handa napisal(a):
>> syzbot is reporting hung task due to flood of
>>
>> tty_warn(tty, "%s: tty->count = 1 port count = %d\n", __func__,
>> port->count);
>>
>> message [1], for ioctl(TIOCVHANGUP) prevents tty_port_close() from
>> decrementing port->count due to tty_hung_up_p() == true.
>>
>> ----------
>> #include <sys/types.h>
>> #include <sys/stat.h>
>> #include <fcntl.h>
>> #include <sys/ioctl.h>
>> #include <unistd.h>
>>
>> int main(int argc, char *argv[])
>> {
>> int i;
>> int fd[10];
>>
>> for (i = 0; i < 10; i++)
>> fd[i] = open("/dev/ttyprintk", O_WRONLY);
>> ioctl(fd[0], TIOCVHANGUP);
>> for (i = 0; i < 10; i++)
>> close(fd[i]);
>> close(open("/dev/ttyprintk", O_WRONLY));
>> return 0;
>> }
>> ----------
>>
>> When TTY hangup happens, port->count needs to be reset via
>> "struct tty_operations"->hangup callback.
>>
>> [1]
>> https://syzkaller.appspot.com/bug?id=39ea6caa479af471183997376dc7e90bc7d64a6a
>>
>> Reported-by: syzbot <syzbot+43e93968b964e369db0b@syzkaller.appspotmail.com>
>> Reported-by: syzbot <syzbot+3ed715090790806d8b18@syzkaller.appspotmail.com>
>> Tested-by: syzbot <syzbot+43e93968b964e369db0b@syzkaller.appspotmail.com>
>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Fixes: 24b4b67d17c308aa ("add ttyprintk driver")
>> ---
>> drivers/char/ttyprintk.c | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
>> index 6a0059e508e3..93f5d11c830b 100644
>> --- a/drivers/char/ttyprintk.c
>> +++ b/drivers/char/ttyprintk.c
>> @@ -158,12 +158,23 @@ static int tpk_ioctl(struct tty_struct *tty,
>> return 0;
>> }
>>
>> +/*
>> + * TTY operations hangup function.
>> + */
>> +static void tpk_hangup(struct tty_struct *tty)
>> +{
>> + struct ttyprintk_port *tpkp = tty->driver_data;
>> +
>> + tty_port_hangup(&tpkp->port);
>> +}
>> +
>> static const struct tty_operations ttyprintk_ops = {
>> .open = tpk_open,
>> .close = tpk_close,
>> .write = tpk_write,
>> .write_room = tpk_write_room,
>> .ioctl = tpk_ioctl,
>> + .hangup = tpk_hangup,
>> };
>>
>> static const struct tty_port_operations null_ops = { };
>
> Using the supplied test code, i've tested the patch on my desktop running the
> 5.4 kernel. After applying the patch, the kernel warnings like "ttyprintk:
> tty_port_close_start: tty->count = 1 port count = 11" do not appear any more,
> when the test code is run.
> I think the patch is ok.

I wonder if the buffer shouldn't be flushed in hangup too? Or better,
the flush moved from tty_ops->close to tty_port->ops->shutdown?

thanks,
--
js
suse labs

\
 
 \ /
  Last update: 2021-04-23 06:23    [W:0.565 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site