Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [High] drm/vkms: broken CRC debugfs unplug handling in vkms_destroy() --
commit 58c6203197ea5aa86a82e01783503c18d44dd2a1 Author: Sebastian Wick <[email protected]> drm/vkms: Use drm_dev_unplug() for ConfigFS device removal This commit switches vkms_destroy() from drm_dev_unregister() to drm_dev_unplug() so that ioctls on open file descriptors are rejected with -ENODEV and in-flight operations guarded by drm_dev_enter()/drm_dev_exit() complete before ConfigFS device removal proceeds. > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c > index 5a640b531d88f..716f9c966c211 100644 > --- a/drivers/gpu/drm/vkms/vkms_drv.c > +++ b/drivers/gpu/drm/vkms/vkms_drv.c > @@ -259,7 +259,7 @@ void vkms_destroy(struct vkms_config *config) > > fdev = config->dev->faux_dev; > > - drm_dev_unregister(&config->dev->drm); > + drm_dev_unplug(&config->dev->drm); > drm_atomic_helper_shutdown(&config->dev->drm); > devres_release_group(&fdev->dev, NULL); [Severity: High] How does this interact with an open CRTC CRC debugfs file descriptor (/sys/kernel/debug/dri/<N>/crtc-<M>/crc/data) when the VKMS device is disabled via ConfigFS? In drivers/gpu/drm/vkms/vkms_composer.c, vkms_set_crc_source() guards the callback with drm_dev_enter(): drivers/gpu/drm/vkms/vkms_composer.c:vkms_set_crc_source() { ... if (!drm_dev_enter(crtc->dev, &idx)) return -ENODEV; ret = vkms_crc_parse_source(src_name, &enabled); vkms_set_composer(out, enabled); drm_dev_exit(idx); return ret; } When the crc/data file descriptor is closed, full_proxy_release() invokes crtc_crc_release() in drivers/gpu/drm/drm_debugfs_crc.c, which calls crtc->funcs->set_crc_source(crtc, NULL). Two issues seem possible here: 1. Unlike /dev/dri/card<N> file descriptors, opening crc/data via crtc_crc_open() does not acquire a drm_dev_get() reference on crtc->dev, and debugfs_remove_recursive() during drm_dev_unregister() does not wait for open file descriptors to close. In vkms_destroy(), drm_dev_unplug() runs synchronize_srcu() before devres_release_group(&fdev->dev, NULL) drops the devm reference via devm_drm_dev_init_release() -> drm_dev_put(). If no /dev/dri/card<N> fd is open (or after it is closed first, such as during process exit when card<N> has a lower fd number than crc/data), drm_dev_release() frees struct vkms_output (embedding struct drm_crtc) and struct vkms_device (embedding struct drm_device). When the crc/data fd is subsequently closed, wouldn't crtc_crc_release() and drm_dev_enter(crtc->dev, &idx) in vkms_set_crc_source() dereference the freed struct drm_crtc and crtc->dev? 2. Conversely, if struct drm_device is still kept alive by an open /dev/dri/card<N> fd when crc/data is closed after drm_dev_unplug() sets dev->unplugged = true, drm_dev_enter(crtc->dev, &idx) in vkms_set_crc_source(crtc, NULL) will return false and exit early with -ENODEV. Doesn't that skip vkms_set_composer(out, false), leaving out->composer_enabled set to true and leaking the vblank reference from drm_crtc_vblank_put(&out->crtc)? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=2
