drm/i915/gtt: Make sure the gen6 ppgtt is bound before first use

As we remove the struct_mutex protection from around the vma pinning,
counters need to be atomic and aware that there may be multiple threads
simultaneously active.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190913064200.24297-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index a09a9b6..e62e9d1 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1790,6 +1790,8 @@ static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
 
        gen6_ppgtt_free_pd(ppgtt);
        free_scratch(vm);
+
+       mutex_destroy(&ppgtt->pin_mutex);
        kfree(ppgtt->base.pd);
 }
 
@@ -1895,7 +1897,7 @@ static struct i915_vma *pd_vma_create(struct gen6_ppgtt *ppgtt, int size)
 int gen6_ppgtt_pin(struct i915_ppgtt *base)
 {
        struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(base);
-       int err;
+       int err = 0;
 
        GEM_BUG_ON(ppgtt->base.vm.closed);
 
@@ -1905,24 +1907,26 @@ int gen6_ppgtt_pin(struct i915_ppgtt *base)
         * (When vma->pin_count becomes atomic, I expect we will naturally
         * need a larger, unpacked, type and kill this redundancy.)
         */
-       if (ppgtt->pin_count++)
+       if (atomic_add_unless(&ppgtt->pin_count, 1, 0))
                return 0;
 
+       if (mutex_lock_interruptible(&ppgtt->pin_mutex))
+               return -EINTR;
+
        /*
         * PPGTT PDEs reside in the GGTT and consists of 512 entries. The
         * allocator works in address space sizes, so it's multiplied by page
         * size. We allocate at the top of the GTT to avoid fragmentation.
         */
-       err = i915_vma_pin(ppgtt->vma,
-                          0, GEN6_PD_ALIGN,
-                          PIN_GLOBAL | PIN_HIGH);
-       if (err)
-               goto unpin;
-
-       return 0;
+       if (!atomic_read(&ppgtt->pin_count)) {
+               err = i915_vma_pin(ppgtt->vma,
+                                  0, GEN6_PD_ALIGN,
+                                  PIN_GLOBAL | PIN_HIGH);
+       }
+       if (!err)
+               atomic_inc(&ppgtt->pin_count);
+       mutex_unlock(&ppgtt->pin_mutex);
 
-unpin:
-       ppgtt->pin_count = 0;
        return err;
 }
 
@@ -1930,22 +1934,20 @@ void gen6_ppgtt_unpin(struct i915_ppgtt *base)
 {
        struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(base);
 
-       GEM_BUG_ON(!ppgtt->pin_count);
-       if (--ppgtt->pin_count)
-               return;
-
-       i915_vma_unpin(ppgtt->vma);
+       GEM_BUG_ON(!atomic_read(&ppgtt->pin_count));
+       if (atomic_dec_and_test(&ppgtt->pin_count))
+               i915_vma_unpin(ppgtt->vma);
 }
 
 void gen6_ppgtt_unpin_all(struct i915_ppgtt *base)
 {
        struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(base);
 
-       if (!ppgtt->pin_count)
+       if (!atomic_read(&ppgtt->pin_count))
                return;
 
-       ppgtt->pin_count = 0;
        i915_vma_unpin(ppgtt->vma);
+       atomic_set(&ppgtt->pin_count, 0);
 }
 
 static struct i915_ppgtt *gen6_ppgtt_create(struct drm_i915_private *i915)
@@ -1958,6 +1960,8 @@ static struct i915_ppgtt *gen6_ppgtt_create(struct drm_i915_private *i915)
        if (!ppgtt)
                return ERR_PTR(-ENOMEM);
 
+       mutex_init(&ppgtt->pin_mutex);
+
        ppgtt_init(&ppgtt->base, &i915->gt);
        ppgtt->base.vm.top = 1;
 

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
index 2017881..8fd2234 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_gtt.h
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
@@ -437,7 +437,9 @@ struct gen6_ppgtt {
        struct i915_vma *vma;
        gen6_pte_t __iomem *pd_addr;
 
-       unsigned int pin_count;
+       atomic_t pin_count;
+       struct mutex pin_mutex;
+
        bool scan_for_unused_pt;
 };