linux-kernel - Re: INFO: task hung in lo

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Message-ID: <CACT4Y+ZaL=zPbb-r7PKvOsY8aBRiMEEHMc+-HVGm+dRTax+DfA@mail.gmail.com>
Date:   Sat, 19 Jan 2019 19:56:00 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Omar Sandoval <osandov@...ndov.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Al Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...com>,
        syzbot 
        <bot+abdba5bc6de135d7622f00756da97998425b6de5@...kaller.appspotmail.com>,
        Jens Axboe <axboe@...nel.dk>, Ming Lei <tom.leiming@...il.com>,
        Hannes Reinecke <hare@...e.de>, shli@...com,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Ingo Molnar <mingo@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>, knikanth@...e.de
Subject: Re: INFO: task hung in lo_ioctl

On Fri, Apr 6, 2018 at 5:59 PM Omar Sandoval <osandov@...ndov.com> wrote:
>
> On Fri, Apr 06, 2018 at 05:43:43PM +0200, Peter Zijlstra wrote:
> > On Fri, Apr 06, 2018 at 10:55:03PM +0900, Tetsuo Handa wrote:
> > > Peter Zijlstra wrote:
> > > > On Fri, Apr 06, 2018 at 09:04:18PM +0900, Tetsuo Handa wrote:
> > >
 > > +       /* Temporary hack for handling lock imbalance. */
> > > > > +       if (__mutex_owner(&lo->lo_ctl_mutex) == current)
> > > > > +               mutex_unlock(&lo->lo_ctl_mutex);
> > > >
> > > > ARGGH.. you didn't read the comment we put on that?
> > > >
> > >
> > > Commit 5b52330bbfe63b33 ("audit: fix auditd/kernel connection state tracking")
> > > is using __mutex_owner(). ;-)
> >
> > That got removed and the warning added.
>
> Seems easy enough to fix without resorting to __mutex_owner() (untested):
>
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 264abaaff662..cee258d12a1e 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1300,12 +1300,13 @@ loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
>  static int
>  loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
>         struct loop_info64 info64;
> -       int err = 0;
> +       int err;
>
> -       if (!arg)
> -               err = -EINVAL;
> -       if (!err)
> -               err = loop_get_status(lo, &info64);
> +       if (!arg) {
> +               mutex_unlock(&lo->lo_ctl_mutex);
> +               return -EINVAL;
> +       }
> +       err = loop_get_status(lo, &info64);
>         if (!err && copy_to_user(arg, &info64, sizeof(info64)))
>                 err = -EFAULT;
>
>
> I'll test it and send it up when I get into the office.


Was this ever submitted? Or some other fix for this?

The bug is still open, but last happened 289 days ago:
https://syzkaller.appspot.com/bug?id=608144371e7fc2cb6285b9ed871fb1eb817a61ce

But it also has 10 duplicates, some of which happened much more recently.
If a fix was submitted, but Reported-by tag wasn't added this open bug
can now mask lots of other new bugs.