Re: [PATCH v1.1] xen/commom/dt-overlay: Fix missing lock when remove the device

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 26 Apr 2024, Henry Wang wrote:
> If CONFIG_DEBUG=y, below assertion will be triggered:
> (XEN) Assertion 'rw_is_locked(&dt_host_lock)' failed at 
> drivers/passthrough/device_tree.c:146
> (XEN) ----[ Xen-4.19-unstable  arm64  debug=y  Not tainted ]----
> (XEN) CPU:    0
> (XEN) PC:     00000a0000257418 iommu_remove_dt_device+0x8c/0xd4
> (XEN) LR:     00000a00002573a0
> (XEN) SP:     00008000fff7fb30
> (XEN) CPSR:   0000000000000249 MODE:64-bit EL2h (Hypervisor, handler)
> [...]
> 
> (XEN) Xen call trace:
> (XEN)    [<00000a0000257418>] iommu_remove_dt_device+0x8c/0xd4 (PC)
> (XEN)    [<00000a00002573a0>] iommu_remove_dt_device+0x14/0xd4 (LR)
> (XEN)    [<00000a000020797c>] dt-overlay.c#remove_node_resources+0x8c/0x90
> (XEN)    [<00000a0000207f14>] dt-overlay.c#remove_nodes+0x524/0x648
> (XEN)    [<00000a0000208460>] dt_overlay_sysctl+0x428/0xc68
> (XEN)    [<00000a00002707f8>] arch_do_sysctl+0x1c/0x2c
> (XEN)    [<00000a0000230b40>] do_sysctl+0x96c/0x9ec
> (XEN)    [<00000a0000271e08>] traps.c#do_trap_hypercall+0x1e8/0x288
> (XEN)    [<00000a0000273490>] do_trap_guest_sync+0x448/0x63c
> (XEN)    [<00000a000025c480>] entry.o#guest_sync_slowpath+0xa8/0xd8
> (XEN)
> (XEN)
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) Assertion 'rw_is_locked(&dt_host_lock)' failed at 
> drivers/passthrough/device_tree.c:146
> (XEN) ****************************************
> 
> This is because iommu_remove_dt_device() is called without taking the
> dt_host_lock. Fix the issue by taking and releasing the lock properly.
> 
> Fixes: 7e5c4a8b86f1 ("xen/arm: Implement device tree node removal 
> functionalities")
> Signed-off-by: Henry Wang <xin.wang2@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> v1.1:
> - Move the unlock position before the check of rc.
> ---
>  xen/common/dt-overlay.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/xen/common/dt-overlay.c b/xen/common/dt-overlay.c
> index 1b197381f6..ab8f43aea2 100644
> --- a/xen/common/dt-overlay.c
> +++ b/xen/common/dt-overlay.c
> @@ -381,7 +381,9 @@ static int remove_node_resources(struct dt_device_node 
> *device_node)
>      {
>          if ( dt_device_is_protected(device_node) )
>          {
> +            write_lock(&dt_host_lock);
>              rc = iommu_remove_dt_device(device_node);
> +            write_unlock(&dt_host_lock);
>              if ( rc < 0 )
>                  return rc;
>          }
> -- 
> 2.34.1
>