Re: [PATCH v2 1/8] xen/common/dt-overlay: Fix lock issue when add/remove the device

[Julien Grall <julien@xxxxxxx>]

Hi Henry,

On 16/05/2024 11:03, 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) 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. dt_host_lock is meant to ensure that the DT node will not
> disappear behind back. So fix the issue by taking the lock as soon as
> getting hold of overlay_node.
>
> Similar issue will be observed in adding the dtbo:
> (XEN) Assertion 'system_state < SYS_STATE_active || rw_is_locked(&dt_host_lock)'
> failed at xen-source/xen/drivers/passthrough/device_tree.c:192
> (XEN) ----[ Xen-4.19-unstable  arm64  debug=y  Not tainted ]----
> [...]
> (XEN) Xen call trace:
> (XEN)    [<00000a00002594f4>] iommu_add_dt_device+0x7c/0x17c (PC)
> (XEN)    [<00000a0000259494>] iommu_add_dt_device+0x1c/0x17c (LR)
> (XEN)    [<00000a0000267db4>] handle_device+0x68/0x1e8
> (XEN)    [<00000a0000208ba8>] dt_overlay_sysctl+0x9d4/0xb84
> (XEN)    [<00000a000027342c>] arch_do_sysctl+0x24/0x38
> (XEN)    [<00000a0000231ac8>] do_sysctl+0x9ac/0xa34
> (XEN)    [<00000a0000274b70>] traps.c#do_trap_hypercall+0x230/0x2dc
> (XEN)    [<00000a0000276330>] do_trap_guest_sync+0x478/0x688
> (XEN)    [<00000a000025e480>] entry.o#guest_sync_slowpath+0xa8/0xd8
>
> This is because the lock is released too early. So fix the issue by
> releasing the lock after handle_device().
>
> Fixes: 7e5c4a8b86f1 ("xen/arm: Implement device tree node removal 
> functionalities")
> Signed-off-by: Henry Wang <xin.wang2@xxxxxxx>
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall