Re: [PATCH] drm: Release driver references to handle before making it available again

On Fri, Jan 08, 2016 at 08:25:07PM +0000, Chris Wilson wrote:

Whilst calling back into the driver, we have to drop the file->table_lock spinlock and so to prevent reusing the closed handle we mark that handle as stale in the idr, perform the callback and then remove the handle. It is then possible for a lookup on that handle to return an error object and so all callers of idr_find(file->object_idr) need to check against IS_ERR_OR_NULL() instead.

• obj = idr_find(&filp->object_idr, handle);
• if (obj == NULL) {

• obj = idr_replace(&filp->object_idr, ERR_PTR(-ENOENT), handle);
• if (IS_ERR(obj)) {

Setting ERR_PTR(-ENOENT) is superfluous. We can just set the entry to NULL as idr_alloc() uses a bitmap to find the new handle. This avoids having to change the callers elsewhere, as idr_find() will then return NULL for the stale handle and the invalid handle. -Chris