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Date:   Sun, 28 Jul 2019 04:36:39 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+36e93b425cd6eb54fcc1@...kaller.appspotmail.com>,
        jasowang@...hat.com, kvm@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        michal.lkml@...kovi.net, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, torvalds@...ux-foundation.org,
        virtualization@...ts.linux-foundation.org,
        yamada.masahiro@...ionext.com
Subject: Re: INFO: rcu detected stall in vhost_worker

On Sat, Jul 27, 2019 at 04:23:23PM +0800, Hillf Danton wrote:
> 
> Fri, 26 Jul 2019 08:26:01 -0700 (PDT)
> > syzbot has bisected this bug to:
> > 
> > commit 0ecfebd2b52404ae0c54a878c872bb93363ada36
> > Author: Linus Torvalds <torvalds@...ux-foundation.org>
> > Date:   Sun Jul 7 22:41:56 2019 +0000
> > 
> >      Linux 5.2
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=118810bfa00000
> > start commit:   13bf6d6a Add linux-next specific files for 20190725
> > git tree:       linux-next
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=8ae987d803395886
> > dashboard link: https://syzkaller.appspot.com/bug?extid=36e93b425cd6eb54fcc1
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15112f3fa00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=131ab578600000
> > 
> > Reported-by: syzbot+36e93b425cd6eb54fcc1@...kaller.appspotmail.com
> > Fixes: 0ecfebd2b524 ("Linux 5.2")
> > 
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -787,7 +787,6 @@ static void vhost_setup_uaddr(struct vho
> 			      size_t size, bool write)
> {
> 	struct vhost_uaddr *addr = &vq->uaddrs[index];
> -	spin_lock(&vq->mmu_lock);
> 
> 	addr->uaddr = uaddr;
> 	addr->size = size;
> @@ -797,7 +796,10 @@ static void vhost_setup_uaddr(struct vho
> static void vhost_setup_vq_uaddr(struct vhost_virtqueue *vq)
> {
> 	spin_lock(&vq->mmu_lock);
> -
> +	/*
> +	 * deadlock if managing to take mmu_lock again while
> +	 * setting up uaddr
> +	 */
> 	vhost_setup_uaddr(vq, VHOST_ADDR_DESC,
> 			  (unsigned long)vq->desc,
> 			  vhost_get_desc_size(vq, vq->num),
> --

Thanks!
I reverted this whole commit.

-- 
MST

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