From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Sjur Brændeland" <sjurbren@gmail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>,
linux-kernel@vger.kernel.org, "Guzman Lugo,
Fernadndo" <fernando.lugo@ti.com>,
virtualization@lists.linux-foundation.org,
Ohad Ben-Cohen <ohad@wizery.com>
Subject: Re: [PATCH] virtio: Don't access device data after unregistration.
Date: Mon, 3 Sep 2012 23:18:47 +0300 [thread overview]
Message-ID: <20120903201847.GC6181@redhat.com> (raw)
In-Reply-To: <CAJK669aRsbOOmjmT+K8OHYvenOhkYWuSOx6nBM7hxC_C4mmw-g@mail.gmail.com>
On Mon, Sep 03, 2012 at 04:50:10PM +0200, Sjur Brændeland wrote:
> Hi Michael,
>
> >> Fix panic in virtio.c when CONFIG_DEBUG_SLAB is set.
> >
> > What's the root cause of the panic?
>
> I believe the cause of the panic is calling
> ida_simple_remove(&virtio_index_ida, dev->index);
> when the dev structure is "poisoned" after kfree.
> It might be the "BUG_ON((int)id < 0)" that bites...
>
> >> Use device_del() and put_device() instead of
> >> device_unregister(), and access device data before
> >> calling put_device().
>
> > Why does this help? Does device_unregister free the
> > device so dev->index access crashes?
>
> Yes, if device ref-count is one when calling unregister
> the device is freed.
Interesting. Where exactly? Note that:
struct rproc_vdev {
struct list_head node;
struct rproc *rproc;
struct virtio_device vdev;
struct rproc_vring vring[RVDEV_NUM_VRINGS];
unsigned long dfeatures;
unsigned long gfeatures;
};
kfree(&proc_vdev->vdev) is unlikely to be the right thing to do.
> > If yes virtio_pci_remove will crash too
> > as it accesses the device after the
> > call to unregister_virtio_device so the
> > fix won't be effective.
>
> I discovered this using the remoteproc framework.
> It might be that device is unregistered with ref-count greater
> than one normally, in that case this bug will not show up.
>
> Regards,
> Sjur
It might be remoteproc has an unrelated bug?
--
MST
next prev parent reply other threads:[~2012-09-03 20:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-03 13:50 [PATCH] virtio: Don't access device data after unregistration sjur.brandeland
2012-09-03 14:14 ` Michael S. Tsirkin
2012-09-03 14:50 ` Sjur Brændeland
2012-09-03 20:18 ` Michael S. Tsirkin [this message]
2012-09-04 12:12 ` Sjur Brændeland
2012-09-04 14:13 ` Michael S. Tsirkin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20120903201847.GC6181@redhat.com \
--to=mst@redhat.com \
--cc=fernando.lugo@ti.com \
--cc=linux-kernel@vger.kernel.org \
--cc=ohad@wizery.com \
--cc=rusty@rustcorp.com.au \
--cc=sjurbren@gmail.com \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).