drm/i915: Trim i915_guc_info() stack usage

i915_guc_info() (part of debugfs output) tries to avoid holding
struct_mutex for a long period by copying onto the stack. This causes a
warning that the stack frame is massive, so stop doing that. We can even
forgo holding the struct_mutex here as that doesn't serialise the values
being read (and the lists used exist for the device lifetime).

v2: Skip printing anything if guc->execbuf_client is disabled (avoids
potential NULL dereference).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20161129121024.22650-2-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index db53fd09f8df2e1501c3bff0ae86ac35d44f5063..144d8066eb59980898105e3ebca0c8226c0b7cec 100644 (file)
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2434,47 +2434,41 @@ static void i915_guc_client_info(struct seq_file *m,
 static int i915_guc_info(struct seq_file *m, void *data)
 {
        struct drm_i915_private *dev_priv = node_to_i915(m->private);
-       struct drm_device *dev = &dev_priv->drm;
-       struct intel_guc guc;
-       struct i915_guc_client client = {};
+       const struct intel_guc *guc = &dev_priv->guc;
        struct intel_engine_cs *engine;
        enum intel_engine_id id;
-       u64 total = 0;
-
-       if (!HAS_GUC_SCHED(dev_priv))
-               return 0;
+       u64 total;
 
-       if (mutex_lock_interruptible(&dev->struct_mutex))
+       if (!guc->execbuf_client) {
+               seq_printf(m, "GuC submission %s\n",
+                          HAS_GUC_SCHED(dev_priv) ?
+                          "disabled" :
+                          "not supported");
                return 0;
-
-       /* Take a local copy of the GuC data, so we can dump it at leisure */
-       guc = dev_priv->guc;
-       if (guc.execbuf_client)
-               client = *guc.execbuf_client;
-
-       mutex_unlock(&dev->struct_mutex);
+       }
 
        seq_printf(m, "Doorbell map:\n");
-       seq_printf(m, "\t%*pb\n", GUC_MAX_DOORBELLS, guc.doorbell_bitmap);
-       seq_printf(m, "Doorbell next cacheline: 0x%x\n\n", guc.db_cacheline);
+       seq_printf(m, "\t%*pb\n", GUC_MAX_DOORBELLS, guc->doorbell_bitmap);
+       seq_printf(m, "Doorbell next cacheline: 0x%x\n\n", guc->db_cacheline);
 
-       seq_printf(m, "GuC total action count: %llu\n", guc.action_count);
-       seq_printf(m, "GuC action failure count: %u\n", guc.action_fail);
-       seq_printf(m, "GuC last action command: 0x%x\n", guc.action_cmd);
-       seq_printf(m, "GuC last action status: 0x%x\n", guc.action_status);
-       seq_printf(m, "GuC last action error code: %d\n", guc.action_err);
+       seq_printf(m, "GuC total action count: %llu\n", guc->action_count);
+       seq_printf(m, "GuC action failure count: %u\n", guc->action_fail);
+       seq_printf(m, "GuC last action command: 0x%x\n", guc->action_cmd);
+       seq_printf(m, "GuC last action status: 0x%x\n", guc->action_status);
+       seq_printf(m, "GuC last action error code: %d\n", guc->action_err);
 
+       total = 0;
        seq_printf(m, "\nGuC submissions:\n");
        for_each_engine(engine, dev_priv, id) {
-               u64 submissions = guc.submissions[id];
+               u64 submissions = guc->submissions[id];
                total += submissions;
                seq_printf(m, "\t%-24s: %10llu, last seqno 0x%08x\n",
-                       engine->name, submissions, guc.last_seqno[id]);
+                       engine->name, submissions, guc->last_seqno[id]);
        }
        seq_printf(m, "\t%s: %llu\n", "Total", total);
 
-       seq_printf(m, "\nGuC execbuf client @ %p:\n", guc.execbuf_client);
-       i915_guc_client_info(m, dev_priv, &client);
+       seq_printf(m, "\nGuC execbuf client @ %p:\n", guc->execbuf_client);
+       i915_guc_client_info(m, dev_priv, guc->execbuf_client);
 
        i915_guc_log_info(m, dev_priv);