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

Henry Wang posted 1 patch 1 week, 2 days ago
Patches applied successfully (tree, apply log)
git fetch https://gitlab.com/xen-project/patchew/xen tags/patchew/20240426015550.577986-1-xin.wang2@amd.com
xen/common/dt-overlay.c | 2 ++
1 file changed, 2 insertions(+)
[PATCH v1.1] xen/commom/dt-overlay: Fix missing lock when remove the device
Posted by Henry Wang 1 week, 2 days ago 
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@amd.com>
---
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
Re: [PATCH v1.1] xen/commom/dt-overlay: Fix missing lock when remove the device
Posted by Julien Grall 1 day, 23 hours ago 
Hi Henry,

On 26/04/2024 02:55, 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@amd.com>
> ---
> 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);

Looking at the code, we are not modifying the device_node, so shouldn't 
this be a read_lock()?

That said, even though either fix your issue, I am not entirely 
convinced this is the correct position for the lock. From my 
understanding, dt_host_lock is meant to ensure that the DT node will not 
disappear behind your back. So in theory, shouldn't the lock be taken as 
soon as you get hold of device_node?

Cheers,

-- 
Julien Grall
Re: [PATCH v1.1] xen/commom/dt-overlay: Fix missing lock when remove the device
Posted by Stefano Stabellini 2 days, 18 hours ago 
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@amd.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
> 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
>

Patchew 2.1-devel-0870f84

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