drm/i915/gem: Serialise debugfs i915_gem_objects with ctx->mutex

commit 4fe9af8e881d946bf60790eeb37a7c4f96e28382 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index e7532e7d74e91bbbddfe0b76ad630a1b1a35d430..0e1f11669b07278d2f6ad4c75fb3fc7317a58d3a 100644 (file)
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -323,6 +323,7 @@ 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),
@@ -343,6 +344,7 @@ 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);