On Sun, 2017-06-04 at 10:32 +0200, Greg Kroah-Hartman wrote:
> On Sat, Jun 03, 2017 at 08:33:52AM +0200, Mike Galbraith wrote:
> > On Wed, 2017-05-31 at 13:21 -0400, Dave Jones wrote:
> > > Just hit this during a trinity run.
> >
> > 925bb1ce47f429f69aad35876df7ecd8c53deb7e is the first bad commit
> > commit 925bb1ce47f429f69aad35876df7ecd8c53deb7e
> > Author: Vegard Nossum <vegard.nos...@oracle.com>
> > Date: Thu May 11 12:18:52 2017 +0200
> >
> > tty: fix port buffer locking
>
> Now reverting this. Oops, sorry, forgot to add Dave and your names to
> the patch revert. The list of people who reported this was really long,
> many thanks for this.
If flush_to_ldisc() is the problem, and taking atomic_write_lock in
that path an acceptable solution, how about do that a bit differently
instead. Lockdep stopped grumbling, vbox seems happy.
925bb1ce47f4 (tty: fix port buffer locking) upset lockdep by holding buf->lock
while acquiring tty->atomic_write_lock. Move acquisition to flush_to_ldisc(),
taking it prior to taking buf->lock. Costs a reference, but appeases lockdep.
Not-so-signed-off-by: /me
---
drivers/tty/tty_buffer.c | 10 ++++++++++
drivers/tty/tty_port.c | 2 --
2 files changed, 10 insertions(+), 2 deletions(-)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -465,7 +465,13 @@ static void flush_to_ldisc(struct work_s
{
struct tty_port *port = container_of(work, struct tty_port, buf.work);
struct tty_bufhead *buf = &port->buf;
+ struct tty_struct *tty = READ_ONCE(port->itty);
+ struct tty_ldisc *disc = NULL;
+ if (tty)
+ disc = tty_ldisc_ref(tty);
+ if (disc)
+ mutex_lock(&tty->atomic_write_lock);
mutex_lock(&buf->lock);
while (1) {
@@ -501,6 +507,10 @@ static void flush_to_ldisc(struct work_s
}
mutex_unlock(&buf->lock);
+ if (disc) {
+ mutex_unlock(&tty->atomic_write_lock);
+ tty_ldisc_deref(disc);
+ }
}
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -34,9 +34,7 @@ static int tty_port_default_receive_buf(
if (!disc)
return 0;
- mutex_lock(&tty->atomic_write_lock);
ret = tty_ldisc_receive_buf(disc, p, (char *)f, count);
- mutex_unlock(&tty->atomic_write_lock);
tty_ldisc_deref(disc);
