Advanced
Mailing List Archive

Mailing List Archive

  1. Home >
  2. Xen>
  3. Devel
[PATCH v1.1] xen/commom/dt-overlay: Fix missing lock when remove the device
xin.wang2 at amd
Apr 25, 2024, 6:55 PM
Post #1 of 4 (7 views)
Permalink
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 [ In reply to ]
sstabellini at kernel
May 2, 2024, 11:11 AM
Post #2 of 4 (3 views)
Permalink
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
>
Re: [PATCH v1.1] xen/commom/dt-overlay: Fix missing lock when remove the device [ In reply to ]
julien at xen
May 3, 2024, 6:04 AM
Post #3 of 4 (3 views)
Permalink
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 [ In reply to ]
xin.wang2 at amd
May 5, 2024, 7:16 PM
Post #4 of 4 (1 views)
Permalink
Hi Julien,

On 5/3/2024 9:04 PM, Julien Grall wrote:
> 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()?

Hmm yes, however after seeing your comment...

>
> 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?

...here. I believe you made a point here so I think I will just move the
write_lock(&dt_host_lock) as soon as getting  overlay_node, i.e. on top
of the call to remove_descendant_nodes_resources(). Therefore we can
solve the assertion issue of this patch together.

Kind regards,
Henry

>
> Cheers,
>

©2024 GT.net. A Gossamer Threads company.
5th Floor, 455 Granville St., Vancouver, BC V6C 1T1, Canada | Legal