From: Jason Gunthorpe <jgg@ziepe.ca>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: kvm@vger.kernel.org
Subject: Re: [PATCH] vfio/pci: Collect hot-reset devices to local buffer
Date: Tue, 7 May 2024 13:54:50 -0300 [thread overview]
Message-ID: <20240507165450.GI4718@ziepe.ca> (raw)
In-Reply-To: <20240503143138.3562116-1-alex.williamson@redhat.com>
On Fri, May 03, 2024 at 08:31:36AM -0600, Alex Williamson wrote:
> Lockdep reports the below circular locking dependency issue. The
> mmap_lock acquisition while holding pci_bus_sem is due to the use of
> copy_to_user() from within a pci_walk_bus() callback.
>
> Building the devices array directly into the user buffer is only for
> convenience. Instead we can allocate a local buffer for the array,
> bounded by the number of devices on the bus/slot, fill the device
> information into this local buffer, then copy it into the user buffer
> outside the bus walk callback.
> Chain exists of:
> &vdev->vma_lock --> pci_bus_sem --> &mm->mmap_lock
>
> Possible unsafe locking scenario:
>
> block dm-0: the capability attribute has been deprecated.
> CPU0 CPU1
> ---- ----
> rlock(&mm->mmap_lock);
> lock(pci_bus_sem);
> lock(&mm->mmap_lock);
> lock(&vdev->vma_lock);
>
> *** DEADLOCK ***
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> drivers/vfio/pci/vfio_pci_core.c | 78 ++++++++++++++++++++------------
> 1 file changed, 49 insertions(+), 29 deletions(-)
I feel like I created this bug...
It is sad we have to allocate kernel memory, but can't think of a
better option.
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Jason
next prev parent reply other threads:[~2024-05-07 16:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-03 14:31 [PATCH] vfio/pci: Collect hot-reset devices to local buffer Alex Williamson
2024-05-07 16:54 ` Jason Gunthorpe [this message]
2024-05-13 7:51 ` Liu, Yi L
2024-05-16 17:44 ` Alex Williamson
2024-05-17 7:40 ` Liu, Yi L
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=20240507165450.GI4718@ziepe.ca \
--to=jgg@ziepe.ca \
--cc=alex.williamson@redhat.com \
--cc=kvm@vger.kernel.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 read-only IMAP folder(s) and NNTP newsgroup(s).