Hi Luben & Iago,
no the code is completely correct and intentional like this.
See the code path which takes the lock in amdgpu_mm_wreg() is a
workaround when the rmmio_size doesn't allow access to the full register
BAR.
In this case the MM_INDEX/MM_DATA registers are used as side path and
because of this we need the lock.
But this case can't happen when you use the MM_INDEX/MM_DATA pair
directly as parameters for the function.
Regards,
Christian.
Am 20.11.19 um 01:23 schrieb Luben Tuikov:
Hi Iago,
Thank you for finding and reporting this potential double lock.
Yes indeed, I see it--it can indeed happen.
Now, since the primitives used--macros using "amdgpu_mm_(r|w)reg\(.*\)"--in
"amdgpu_device_vram_access()" do use their own register-access spinlocks,
it maybe wise to remove the spinlock take/release in "amdgpu_device_vram_access()".
We'll look into it and possibly submit another patch.
Thanks again.
Regards,
Luben
On 2019-11-16 11:21 a.m., Iago Abal wrote:
Hi,
With the help of a static bug finder (EBA - https://github.com/IagoAbal/eba) I have found a potential double lock in Linux Next tag next-20191115, file drivers/gpu/drm/amd/amdgpu/amdgpu_device.c.
This bug seems to be introduced by commit
e35e2b117f4 ("drm/amdgpu: add a generic fb accessing helper function(v3)").
The steps to reproduce it would be:
1. Start in function `amdgpu_device_vram_access`.
2. Enter for-loop `for (last += pos; pos <= last; pos += 4)`.
3. First lock: `spin_lock_irqsave(&adev->mmio_idx_lock, flags)`.
4. Call to `WREG32_NO_KIQ(mmMM_INDEX, ((uint32_t)pos) | 0x80000000)`.
5. Note `#define WREG32_NO_KIQ(reg, v) amdgpu_mm_wreg(adev, (reg), (v), AMDGPU_REGS_NO_KIQ)`.
6. Continue in function `amdgpu_mm_wreg`.
7. Take else-branch in the third if-statement.
8. Double lock: `spin_lock_irqsave(&adev->mmio_idx_lock, flags)`.
I think the control flow could reach that second lock, but you may know better.
Hope it helps!
-- iago
_______________________________________________
amd-gfx mailing list
amd-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
_______________________________________________
amd-gfx mailing list
amd-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
