[PATCH 1/3] dma_resv: prime lockdep annotations

* [PATCH 1/3] dma_resv: prime lockdep annotations
@ 2019-08-21 21:50 Daniel Vetter
       [not found] ` <20190821215030.31660-1-daniel.vetter-/w4YWyX8dFk@public.gmane.org>
                   ` (10 more replies)
  0 siblings, 11 replies; 27+ messages in thread
From: Daniel Vetter @ 2019-08-21 21:50 UTC (permalink / raw)
  To: DRI Development
  Cc: Rob Herring, Thomas Hellstrom, Tomeu Vizoso, Daniel Vetter,
	Intel Graphics Development, VMware Graphics, Gerd Hoffmann,
	Thomas Zimmermann, Daniel Vetter, Alex Deucher, Dave Airlie,
	Christian König, Ben Skeggs

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 <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>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 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
+
 /**
  * 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);
 
-- 
2.23.0.rc1

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