Re: [PATCH] dma_resv: prime lockdep annotations

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On 8/22/19 3:07 PM, 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@xxxxxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Rob Herring <robh@xxxxxxxxxx>
Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
Cc: Eric Anholt <eric@xxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
Cc: "VMware Graphics" <linux-graphics-maintainer@xxxxxxxxxx>
Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Tested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
  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 42a8f3f11681..97c4c4812d08 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);


I took a quick look into using lockdep macros replacing the actual locks: Something along the lines of

lock_acquire(mm->mmap_sem.dep_map, 0, 0, 1, 1, NULL, _THIS_IP_);
+	ww_mutex_lock(&obj.lock, NULL);
lock_acquire(obj.lock.dep_map, 0, 0, 0, 1, NULL, _THIS_IP_);
+	fs_reclaim_acquire(GFP_KERNEL);
+	fs_reclaim_release(GFP_KERNEL);
+	ww_mutex_unlock(&obj.lock);

lock_release(obj.lock.dep_map, 0, _THIS_IP_);

+	up_read(&mm->mmap_sem);

lock_release(obj.lock.dep_map, 0, _THIS_IP_);

Either way is fine with me, though.

Reviewed-by: Thomas Hellström <thellstrom@xxxxxxxxxx>


+	
+	mmput(mm);
+}
+subsys_initcall(dma_resv_lockdep);
+#endif
+
  /**
   * dma_resv_init - initialize a reservation object
   * @obj: the reservation object


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