From 4fe9af8e881d946bf60790eeb37a7c4f96e28382 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 23 Jul 2020 18:21:19 +0100
Subject: [PATCH] drm/i915/gem: Serialise debugfs i915_gem_objects with ctx->mutex
Git-commit: 4fe9af8e881d946bf60790eeb37a7c4f96e28382
Patch-mainline: v5.10-rc1
No-fix: 102f5aa491f262c818e607fc4fee08a724a76c69
References: git-fixes

Since the debugfs may peek into the GEM contexts as the corresponding
client/fd is being closed, we may try and follow a dangling pointer.
However, the context closure itself is serialised with the ctx->mutex,
so if we hold that mutex as we inspect the state coupled in the context,
we know the pointers within the context are stable and will remain valid
as we inspect their tables.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: CQ Tang <cq.tang@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200723172119.17649-3-chris@chris-wilson.co.uk
(cherry picked from commit 102f5aa491f262c818e607fc4fee08a724a76c69)

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_debugfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 784219962193..ea469168cd44 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -326,6 +326,7 @@ static void print_context_stats(struct seq_file *m,
 		}
 		i915_gem_context_unlock_engines(ctx);
 
+		mutex_lock(&ctx->mutex);
 		if (!IS_ERR_OR_NULL(ctx->file_priv)) {
 			struct file_stats stats = {
 				.vm = rcu_access_pointer(ctx->vm),
@@ -346,6 +347,7 @@ static void print_context_stats(struct seq_file *m,
 
 			print_file_stats(m, name, stats);
 		}
+		mutex_unlock(&ctx->mutex);
 
 		spin_lock(&i915->gem.contexts.lock);
 		list_safe_reset_next(ctx, cn, link);
-- 
2.26.2