Re: REGRESSION: lockdep warning triggered by 15b9ce7ecd: virtio_balloon: stay awake while adjusting balloon

[Theodore Ts'o]

On Wed, Jan 10, 2024 at 03:11:01AM -0500, Michael S. Tsirkin wrote:
> On Mon, Jan 08, 2024 at 04:50:15PM -0500, Theodore Ts'o wrote:
> > Hi, while doing final testing before sending a pull request, I merged
> > in linux-next, and commit 5b9ce7ecd7: virtio_balloon: stay awake while
> > adjusting balloon seems to be causing a lockdep warning (see attached)
> > when running gce-xfstests on a Google Compute Engine e2 VM.  I was not
> > able to trigger it using kvm-xfstests, but the following command:
> > "gce-xfstests -C 10 ext4/4k generic/476) was sufficient to triger the
> > problem.   For more information please see [1] and [2].
> > 
> > [1] 
> > https://github.com/tytso/xfstests-bld/blob/master/Documentation/gce-xfstests.md
> > [2] https://thunk.org/gce-xfstests
> > 
> > I found it by looking at the git logs, and this commit aroused my
> > suspicions, and I further testing showed that the lockdep warning was
> > reproducible with this commit, but not when testing with the
> > immediately preceeding commit (15b9ce7ecd^).
> > 
> > Cheers,
> 
> 
> Thanks a lot for the report!
> I pushed a fixed patch out (tree rebased).
> Would be great if you can confirm it's allright now.

I manually fixed up the white-space issues with the patch last night,
and verified that it fixed it for me with an overnight test run.  (My
patch was versus next-20240109, and then I tested with ext4/dev merged
in.  Previously I had noted the problem with next-20240107 with
ext4/dev merged in.)

Thanks,

                                        - Ted


>From 98097bbd4fe2e15db8fa357aa6e29435cb62e450 Mon Sep 17 00:00:00 2001
From: David Stevens <steve...@chromium.org>
Date: Tue, 9 Jan 2024 14:41:21 +0900
Subject: [PATCH] virtio_balloon: Fix interrupt context deadlock

Use _irq spinlock functions with the adjustment_lock, since
start_update_balloon_size needs to acquire it in an interrupt context.

Fixes: 5b9ce7ecd715 ("virtio_balloon: stay awake while adjusting balloon")
Reported-by: Theodore Ts'o <ty...@mit.edu>
Tested-by: Theodore Ts'o <ty...@mit.edu>
Signed-off-by: David Stevens <steve...@chromium.org>
Signed-off-by: Theodore Ts'o <ty...@mit.edu>
---
 drivers/virtio/virtio_balloon.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index aa6a1a649ad6..1f5b3dd31fcf 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -459,12 +459,12 @@ static void start_update_balloon_size(struct 
virtio_balloon *vb)
 
 static void end_update_balloon_size(struct virtio_balloon *vb)
 {
-       spin_lock(&vb->adjustment_lock);
+       spin_lock_irq(&vb->adjustment_lock);
        if (!vb->adjustment_signal_pending && vb->adjustment_in_progress) {
                vb->adjustment_in_progress = false;
                pm_relax(vb->vdev->dev.parent);
        }
-       spin_unlock(&vb->adjustment_lock);
+       spin_unlock_irq(&vb->adjustment_lock);
 }
 
 static void virtballoon_changed(struct virtio_device *vdev)
@@ -506,9 +506,9 @@ static void update_balloon_size_func(struct work_struct 
*work)
        vb = container_of(work, struct virtio_balloon,
                          update_balloon_size_work);
 
-       spin_lock(&vb->adjustment_lock);
+       spin_lock_irq(&vb->adjustment_lock);
        vb->adjustment_signal_pending = false;
-       spin_unlock(&vb->adjustment_lock);
+       spin_unlock_irq(&vb->adjustment_lock);
 
        diff = towards_target(vb);
 
-- 
2.43.0