Re: [PATCH v10 06/69] drm/probe-helper: Introduce .force_ctx() connector callback

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Modifying `connector->status` before `force_ctx()` can return `-EDEADLK` causes subsequent retries to incorrectly evaluate `old_status == connector->status`, silently skipping the hotplug event.
--

--- Patch [6]: [PATCH v10 06/69] drm/probe-helper: Introduce .force_ctx() connector callback ---
commit b08054d3073ea6707b0fe9e517dde416f7e5c8b6
Author: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>

drm/probe-helper: Introduce .force_ctx() connector callback

This commit introduces a force_ctx() variant to the connector helper
functions, taking a modeset acquire context and returning an error code
so that -EDEADLK can propagate. It takes precedence over the existing
force() callback when both are implemented.

> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index e26ead5b5e589..918255bcfa096 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c

[ ... ]

> @@ -592,8 +593,19 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  			connector->status = connector_status_connected;
>  		else
>  			connector->status = connector_status_disconnected;
> -		if (connector->funcs->force)
> +
> +		if (funcs && funcs->force_ctx) {
> +			ret = funcs->force_ctx(connector, &ctx);
> +			if (ret == -EDEADLK) {
> +				drm_modeset_backoff(&ctx);
> +				goto retry;

[Severity: Medium]
Does modifying connector->status before force_ctx() cause hotplug events
to be dropped on lock contention?

If funcs->force_ctx() returns -EDEADLK, the code branches to the retry
label. During the retry loop, old_status is assigned the current
connector->status:

drm_helper_probe_single_connector_modes() {
retry:
        ...
        old_status = connector->status;

Since connector->status was already updated prior to the failed attempt,
old_status will equal the new status. When the lock is finally acquired
after the retry, the old_status != connector->status check later in the
function evaluates to false, causing the hotplug event detection logic
to be silently skipped.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260731-dw-hdmi-qp-scramb-v10-0-294364b2cf15@collabora.com?part=6