Messages in this thread | | | Subject | Re: [PATCH] ttyprintk: Add TTY hangup callback. | From | Samo Pogačnik <> | Date | Sun, 18 Apr 2021 13:16:05 +0200 |
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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.
best regards, Samo
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