RE: [PATCH v2 vfio 2/3] pds/vfio: Fix mutex lock->magic != lock warning

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Brett Creeley [mailto:brett.creeley@xxxxxxx]
> Sent: 12 October 2023 00:01
> To: jgg@xxxxxxxx; yishaih@xxxxxxxxxx; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@xxxxxxxxxx>; kevin.tian@xxxxxxxxx;
> alex.williamson@xxxxxxxxxx; dan.carpenter@xxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> brett.creeley@xxxxxxx; shannon.nelson@xxxxxxx
> Subject: [PATCH v2 vfio 2/3] pds/vfio: Fix mutex lock->magic != lock warning
> 
> The following BUG was found when running on a kernel with
> CONFIG_DEBUG_MUTEXES=y set:
> 
> DEBUG_LOCKS_WARN_ON(lock->magic != lock)
> RIP: 0010:mutex_trylock+0x10d/0x120
> Call Trace:
>  <TASK>
>  ? __warn+0x85/0x140
>  ? mutex_trylock+0x10d/0x120
>  ? report_bug+0xfc/0x1e0
>  ? handle_bug+0x3f/0x70
>  ? exc_invalid_op+0x17/0x70
>  ? asm_exc_invalid_op+0x1a/0x20
>  ? mutex_trylock+0x10d/0x120
>  ? mutex_trylock+0x10d/0x120
>  pds_vfio_reset+0x3a/0x60 [pds_vfio_pci]
>  pci_reset_function+0x4b/0x70
>  reset_store+0x5b/0xa0
>  kernfs_fop_write_iter+0x137/0x1d0
>  vfs_write+0x2de/0x410
>  ksys_write+0x5d/0xd0
>  do_syscall_64+0x3b/0x90
>  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> 
> As shown, lock->magic != lock. This is because
> mutex_init(&pds_vfio->state_mutex) is called in the VFIO open path. So,
> if a reset is initiated before the VFIO device is opened the mutex will
> have never been initialized. Fix this by calling
> mutex_init(&pds_vfio->state_mutex) in the VFIO init path.
> 
> Also, don't destroy the mutex on close because the device may
> be re-opened, which would cause mutex to be uninitialized. Fix this by
> implementing a driver specific vfio_device_ops.release callback that
> destroys the mutex before calling vfio_pci_core_release_dev().
> 
> Signed-off-by: Brett Creeley <brett.creeley@xxxxxxx>
> Reviewed-by: Shannon Nelson <shannon.nelson@xxxxxxx>

Reviewed-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>

Looks like mutex destruction logic needs to be added to HiSilicon driver as well.
>From a quick look mlx5 also doesn't destroy the state_mutex.

Thanks,
Shameer
 
> ---
>  drivers/vfio/pci/pds/vfio_dev.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/pci/pds/vfio_dev.c b/drivers/vfio/pci/pds/vfio_dev.c
> index c351f588fa13..306b1c25f016 100644
> --- a/drivers/vfio/pci/pds/vfio_dev.c
> +++ b/drivers/vfio/pci/pds/vfio_dev.c
> @@ -155,6 +155,7 @@ static int pds_vfio_init_device(struct vfio_device
> *vdev)
> 
>  	pds_vfio->vf_id = vf_id;
> 
> +	mutex_init(&pds_vfio->state_mutex);
>  	spin_lock_init(&pds_vfio->reset_lock);
> 
>  	vdev->migration_flags = VFIO_MIGRATION_STOP_COPY |
> VFIO_MIGRATION_P2P;
> @@ -170,6 +171,16 @@ static int pds_vfio_init_device(struct vfio_device
> *vdev)
>  	return 0;
>  }
> 
> +static void pds_vfio_release_device(struct vfio_device *vdev)
> +{
> +	struct pds_vfio_pci_device *pds_vfio =
> +		container_of(vdev, struct pds_vfio_pci_device,
> +			     vfio_coredev.vdev);
> +
> +	mutex_destroy(&pds_vfio->state_mutex);
> +	vfio_pci_core_release_dev(vdev);
> +}
> +
>  static int pds_vfio_open_device(struct vfio_device *vdev)
>  {
>  	struct pds_vfio_pci_device *pds_vfio =
> @@ -181,7 +192,6 @@ static int pds_vfio_open_device(struct vfio_device
> *vdev)
>  	if (err)
>  		return err;
> 
> -	mutex_init(&pds_vfio->state_mutex);
>  	pds_vfio->state = VFIO_DEVICE_STATE_RUNNING;
>  	pds_vfio->deferred_reset_state = VFIO_DEVICE_STATE_RUNNING;
> 
> @@ -201,14 +211,13 @@ static void pds_vfio_close_device(struct
> vfio_device *vdev)
>  	pds_vfio_put_save_file(pds_vfio);
>  	pds_vfio_dirty_disable(pds_vfio, true);
>  	mutex_unlock(&pds_vfio->state_mutex);
> -	mutex_destroy(&pds_vfio->state_mutex);
>  	vfio_pci_core_close_device(vdev);
>  }
> 
>  static const struct vfio_device_ops pds_vfio_ops = {
>  	.name = "pds-vfio",
>  	.init = pds_vfio_init_device,
> -	.release = vfio_pci_core_release_dev,
> +	.release = pds_vfio_release_device,
>  	.open_device = pds_vfio_open_device,
>  	.close_device = pds_vfio_close_device,
>  	.ioctl = vfio_pci_core_ioctl,
> --
> 2.17.1