Re: [PATCH 1/3] dma_resv: prime lockdep annotations

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Nov 14, 2019 at 11:50:28AM +0000, Steven Price wrote:
> On 11/11/2019 15:42, Daniel Vetter wrote:
> > On Mon, Nov 11, 2019 at 2:11 PM Steven Price <steven.price@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@kernel.org>
> >>> Cc: Alex Deucher <alexander.deucher@amd.com>
> >>> Cc: Christian König <christian.koenig@amd.com>
> >>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> >>> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> >>> Cc: Rob Herring <robh@kernel.org>
> >>> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> >>> Cc: Eric Anholt <eric@anholt.net>
> >>> Cc: Dave Airlie <airlied@redhat.com>
> >>> Cc: Gerd Hoffmann <kraxel@redhat.com>
> >>> Cc: Ben Skeggs <bskeggs@redhat.com>
> >>> Cc: "VMware Graphics" <linux-graphics-maintainer@vmware.com>
> >>> Cc: Thomas Hellstrom <thellstrom@vmware.com>
> >>> Reviewed-by: Christian König <christian.koenig@amd.com>
> >>> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> >>> Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
> >>> Signed-off-by: Daniel Vetter <daniel.vetter@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@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

Since this seems a bit stuck in processing I went ahead and merged your
fix meanwhile.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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