lkml.org 
[lkml]   [2018]   [Mar]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.4 06/63] drm: Allow determining if current task is output poll worker
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Lukas Wunner <lukas@wunner.de>

    commit 25c058ccaf2ebbc3e250ec1e199e161f91fe27d4 upstream.

    Introduce a helper to determine if the current task is an output poll
    worker.

    This allows us to fix a long-standing deadlock in several DRM drivers
    wherein the ->runtime_suspend callback waits for the output poll worker
    to finish and the worker in turn calls a ->detect callback which waits
    for runtime suspend to finish. The ->detect callback is invoked from
    multiple call sites and waiting for runtime suspend to finish is the
    correct thing to do except if it's executing in the context of the
    worker.

    v2: Expand kerneldoc to specifically mention deadlock between
    output poll worker and autosuspend worker as use case. (Lyude)

    Cc: Dave Airlie <airlied@redhat.com>
    Cc: Ben Skeggs <bskeggs@redhat.com>
    Cc: Alex Deucher <alexander.deucher@amd.com>
    Reviewed-by: Lyude Paul <lyude@redhat.com>
    Signed-off-by: Lukas Wunner <lukas@wunner.de>
    Link: https://patchwork.freedesktop.org/patch/msgid/3549ce32e7f1467102e70d3e9cbf70c46bfe108e.1518593424.git.lukas@wunner.de
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/drm_probe_helper.c | 20 ++++++++++++++++++++
    include/drm/drm_crtc_helper.h | 1 +
    2 files changed, 21 insertions(+)

    --- a/drivers/gpu/drm/drm_probe_helper.c
    +++ b/drivers/gpu/drm/drm_probe_helper.c
    @@ -412,6 +412,26 @@ out:
    }

    /**
    + * drm_kms_helper_is_poll_worker - is %current task an output poll worker?
    + *
    + * Determine if %current task is an output poll worker. This can be used
    + * to select distinct code paths for output polling versus other contexts.
    + *
    + * One use case is to avoid a deadlock between the output poll worker and
    + * the autosuspend worker wherein the latter waits for polling to finish
    + * upon calling drm_kms_helper_poll_disable(), while the former waits for
    + * runtime suspend to finish upon calling pm_runtime_get_sync() in a
    + * connector ->detect hook.
    + */
    +bool drm_kms_helper_is_poll_worker(void)
    +{
    + struct work_struct *work = current_work();
    +
    + return work && work->func == output_poll_execute;
    +}
    +EXPORT_SYMBOL(drm_kms_helper_is_poll_worker);
    +
    +/**
    * drm_kms_helper_poll_disable - disable output polling
    * @dev: drm_device
    *
    --- a/include/drm/drm_crtc_helper.h
    +++ b/include/drm/drm_crtc_helper.h
    @@ -241,5 +241,6 @@ extern void drm_kms_helper_hotplug_event
    extern void drm_kms_helper_poll_disable(struct drm_device *dev);
    extern void drm_kms_helper_poll_enable(struct drm_device *dev);
    extern void drm_kms_helper_poll_enable_locked(struct drm_device *dev);
    +extern bool drm_kms_helper_is_poll_worker(void);

    #endif

    \
     
     \ /
      Last update: 2018-03-16 18:35    [W:2.132 / U:0.112 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site