[PATCH 1/3] dma_resv: prime lockdep annotations

[Steven Price]

On 11/11/2019 15:42, Daniel Vetter wrote:
> On Mon, Nov 11, 2019 at 2:11 PM Steven Price <steven.price at arm.com> wrote:
>>
>> On 04/11/2019 17:37, Daniel Vetter wrote:
>>> Full audit of everyone:
>>>
>>> - i915, radeon, amdgpu should be clean per their maintainers.
>>>
>>> - vram helpers should be fine, they don't do command submission, so
>>>   really no business holding struct_mutex while doing copy_*_user. But
>>>   I haven't checked them all.
>>>
>>> - panfrost seems to dma_resv_lock only in panfrost_job_push, which
>>>   looks clean.
>>>
>>> - v3d holds dma_resv locks in the tail of its v3d_submit_cl_ioctl(),
>>>   copying from/to userspace happens all in v3d_lookup_bos which is
>>>   outside of the critical section.
>>>
>>> - vmwgfx has a bunch of ioctls that do their own copy_*_user:
>>>   - vmw_execbuf_process: First this does some copies in
>>>     vmw_execbuf_cmdbuf() and also in the vmw_execbuf_process() itself.
>>>     Then comes the usual ttm reserve/validate sequence, then actual
>>>     submission/fencing, then unreserving, and finally some more
>>>     copy_to_user in vmw_execbuf_copy_fence_user. Glossing over tons of
>>>     details, but looks all safe.
>>>   - vmw_fence_event_ioctl: No ttm_reserve/dma_resv_lock anywhere to be
>>>     seen, seems to only create a fence and copy it out.
>>>   - a pile of smaller ioctl in vmwgfx_ioctl.c, no reservations to be
>>>     found there.
>>>   Summary: vmwgfx seems to be fine too.
>>>
>>> - virtio: There's virtio_gpu_execbuffer_ioctl, which does all the
>>>   copying from userspace before even looking up objects through their
>>>   handles, so safe. Plus the getparam/getcaps ioctl, also both safe.
>>>
>>> - qxl only has qxl_execbuffer_ioctl, which calls into
>>>   qxl_process_single_command. There's a lovely comment before the
>>>   __copy_from_user_inatomic that the slowpath should be copied from
>>>   i915, but I guess that never happened. Try not to be unlucky and get
>>>   your CS data evicted between when it's written and the kernel tries
>>>   to read it. The only other copy_from_user is for relocs, but those
>>>   are done before qxl_release_reserve_list(), which seems to be the
>>>   only thing reserving buffers (in the ttm/dma_resv sense) in that
>>>   code. So looks safe.
>>>
>>> - A debugfs file in nouveau_debugfs_pstate_set() and the usif ioctl in
>>>   usif_ioctl() look safe. nouveau_gem_ioctl_pushbuf() otoh breaks this
>>>   everywhere and needs to be fixed up.
>>>
>>> v2: Thomas pointed at that vmwgfx calls dma_resv_init while it holds a
>>> dma_resv lock of a different object already. Christian mentioned that
>>> ttm core does this too for ghost objects. intel-gfx-ci highlighted
>>> that i915 has similar issues.
>>>
>>> Unfortunately we can't do this in the usual module init functions,
>>> because kernel threads don't have an ->mm - we have to wait around for
>>> some user thread to do this.
>>>
>>> Solution is to spawn a worker (but only once). It's horrible, but it
>>> works.
>>>
>>> v3: We can allocate mm! (Chris). Horrible worker hack out, clean
>>> initcall solution in.
>>>
>>> v4: Annotate with __init (Rob Herring)
>>>
>>> Cc: Rob Herring <robh at kernel.org>
>>> Cc: Alex Deucher <alexander.deucher at amd.com>
>>> Cc: Christian König <christian.koenig at amd.com>
>>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>>> Cc: Thomas Zimmermann <tzimmermann at suse.de>
>>> Cc: Rob Herring <robh at kernel.org>
>>> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
>>> Cc: Eric Anholt <eric at anholt.net>
>>> Cc: Dave Airlie <airlied at redhat.com>
>>> Cc: Gerd Hoffmann <kraxel at redhat.com>
>>> Cc: Ben Skeggs <bskeggs at redhat.com>
>>> Cc: "VMware Graphics" <linux-graphics-maintainer at vmware.com>
>>> Cc: Thomas Hellstrom <thellstrom at vmware.com>
>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
>>> Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
>>> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
>>> ---
>>>  drivers/dma-buf/dma-resv.c | 24 ++++++++++++++++++++++++
>>>  1 file changed, 24 insertions(+)
>>>
>>> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
>>> index 709002515550..a05ff542be22 100644
>>> --- a/drivers/dma-buf/dma-resv.c
>>> +++ b/drivers/dma-buf/dma-resv.c
>>> @@ -34,6 +34,7 @@
>>>
>>>  #include <linux/dma-resv.h>
>>>  #include <linux/export.h>
>>> +#include <linux/sched/mm.h>
>>>
>>>  /**
>>>   * DOC: Reservation Object Overview
>>> @@ -95,6 +96,29 @@ static void dma_resv_list_free(struct dma_resv_list *list)
>>>       kfree_rcu(list, rcu);
>>>  }
>>>
>>> +#if IS_ENABLED(CONFIG_LOCKDEP)
>>> +static void __init dma_resv_lockdep(void)
>>> +{
>>> +     struct mm_struct *mm = mm_alloc();
>>> +     struct dma_resv obj;
>>> +
>>> +     if (!mm)
>>> +             return;
>>> +
>>> +     dma_resv_init(&obj);
>>> +
>>> +     down_read(&mm->mmap_sem);
>>> +     ww_mutex_lock(&obj.lock, NULL);
>>> +     fs_reclaim_acquire(GFP_KERNEL);
>>> +     fs_reclaim_release(GFP_KERNEL);
>>> +     ww_mutex_unlock(&obj.lock);
>>> +     up_read(&mm->mmap_sem);
>>> +
>>
>> Nit: trailing whitespace
>>
>>> +     mmput(mm);
>>> +}
>>> +subsys_initcall(dma_resv_lockdep);
>>
>> This expects a function returning int, but dma_resv_lockdep() is void.
>> Causing:
>>
>> drivers/dma-buf/dma-resv.c:119:17: error: initialization of ‘initcall_t’
>> {aka ‘int (*)(void)’} from incompatible pointer type ‘void (*)(void)’
>> [-Werror=incompatible-pointer-types]
>>  subsys_initcall(dma_resv_lockdep);
>>
>> The below fixes it for me.
> 
> Uh, so _that_ was what the 0day thing was all about, I totally misread
> that completely. Thanks for the patch.
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> Aside, do you need commit rights for pushing this kind of stuff?

I guess it's about time I got round to requesting that:

https://gitlab.freedesktop.org/freedesktop/freedesktop/issues/208

Thanks,

Steve