[1/3] dma_resv: prime lockdep annotations

Commit Message

Daniel Vetter Aug. 21, 2019, 9:50 p.m. UTC

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.

Cc: Alex Deucher <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: Chris Wilson <[e-mail]>
Cc: Thomas Zimmermann <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Tomeu Vizoso <[e-mail]>
Cc: Eric Anholt <[e-mail]>
Cc: Dave Airlie <[e-mail]>
Cc: Gerd Hoffmann <[e-mail]>
Cc: Ben Skeggs <[e-mail]>
Cc: "VMware Graphics" <[e-mail]>
Cc: Thomas Hellstrom <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
---
 drivers/dma-buf/dma-resv.c | 42 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

Comments

Chris Wilson Aug. 21, 2019, 10:20 p.m. UTC | #1

Quoting Daniel Vetter (2019-08-21 22:50:28)
> 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.
> 
> Cc: Alex Deucher <[e-mail]>
> Cc: Christian König <[e-mail]>
> Cc: Chris Wilson <[e-mail]>
> Cc: Thomas Zimmermann <[e-mail]>
> Cc: Rob Herring <[e-mail]>
> Cc: Tomeu Vizoso <[e-mail]>
> Cc: Eric Anholt <[e-mail]>
> Cc: Dave Airlie <[e-mail]>
> Cc: Gerd Hoffmann <[e-mail]>
> Cc: Ben Skeggs <[e-mail]>
> Cc: "VMware Graphics" <[e-mail]>
> Cc: Thomas Hellstrom <[e-mail]>
> Signed-off-by: Daniel Vetter <[e-mail]>
> ---
>  drivers/dma-buf/dma-resv.c | 42 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 42a8f3f11681..29988b1564c1 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 +96,28 @@ static void dma_resv_list_free(struct dma_resv_list *list)
>         kfree_rcu(list, rcu);
>  }
>  
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> +struct lockdep_work {
> +       struct work_struct work;
> +       struct dma_resv obj;
> +       struct mm_struct *mm;
> +} lockdep_work;
> +
> +void lockdep_work_fn(struct work_struct *work)
> +{
> +       dma_resv_init(&lockdep_work.obj);
> +
> +       down_read(&lockdep_work.mm->mmap_sem);
> +       ww_mutex_lock(&lockdep_work.obj.lock, NULL);
> +       fs_reclaim_acquire(GFP_KERNEL);
> +       fs_reclaim_release(GFP_KERNEL);
> +       ww_mutex_unlock(&lockdep_work.obj.lock);
> +       up_read(&lockdep_work.mm->mmap_sem);
> +       
> +       mmput(lockdep_work.mm);
> +}
> +#endif

#if IS_ENABLED(CONFIG_LOCKDEP)
static void dma_resv_lockmap(void)
{
	struct mm_struct *mm = alloc_mm();
	struct dma_resv obj;

	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);

	mmput(mm);
}
core_initcall(dma_resv_lockmap);
#endif

as a thought.
-Chris

Patch

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 42a8f3f11681..29988b1564c1 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 +96,28 @@  static void dma_resv_list_free(struct dma_resv_list *list)
 	kfree_rcu(list, rcu);
 }
 
+#if IS_ENABLED(CONFIG_LOCKDEP)
+struct lockdep_work {
+	struct work_struct work;
+	struct dma_resv obj;
+	struct mm_struct *mm;
+} lockdep_work;
+
+void lockdep_work_fn(struct work_struct *work)
+{
+	dma_resv_init(&lockdep_work.obj);
+
+	down_read(&lockdep_work.mm->mmap_sem);
+	ww_mutex_lock(&lockdep_work.obj.lock, NULL);
+	fs_reclaim_acquire(GFP_KERNEL);
+	fs_reclaim_release(GFP_KERNEL);
+	ww_mutex_unlock(&lockdep_work.obj.lock);
+	up_read(&lockdep_work.mm->mmap_sem);
+	
+	mmput(lockdep_work.mm);
+}
+#endif
+
 /**
  * dma_resv_init - initialize a reservation object
  * @obj: the reservation object
@@ -107,6 +130,25 @@  void dma_resv_init(struct dma_resv *obj)
 			&reservation_seqcount_class);
 	RCU_INIT_POINTER(obj->fence, NULL);
 	RCU_INIT_POINTER(obj->fence_excl, NULL);
+
+#if IS_ENABLED(CONFIG_LOCKDEP)
+	if (current->mm) {
+		static atomic_t lockdep_primed;
+
+		/*
+		 * This gets called from all kinds of places, launch a worker.
+		 * Usual init sections don't work for kernel threads lack an
+		 * ->mm.
+		 */
+		if (atomic_cmpxchg(&lockdep_primed, 0, 1) == 0) {
+			INIT_WORK(&lockdep_work.work, lockdep_work_fn);
+			lockdep_work.mm = current->mm;
+			mmget(lockdep_work.mm);
+
+			schedule_work(&lockdep_work.work);
+		}
+	}
+#endif
 }
 EXPORT_SYMBOL(dma_resv_init);