Re: [Intel-gfx] [PATCH 3/3] drm/i915/gem: Serialise debugfs i915_gem_objects with ctx->mutex

On 23/07/2020 18:21, Chris Wilson wrote:

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

---

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);

Hm this apparently never got it's r-b and so got re-discovered in the field. +Nikunj

Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com

Regards,

Tvrtko