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    Subject[PATCH 0/1] [RFC] DRM locking issues during early open
    We have been carrying a (rather poor) patch for an issue we identified in
    the DRM driver. This issue is triggered when a DRM device is initialising
    and userspace attempts to open it, typically in response to the sysfs
    device added event. Basically we allocate the minor numbers making
    the device available, and then call the drm load callback. Until this
    completes the device is really not ready and these early opens typically
    lead to oopses.

    We have been using the following patch to avoid this by marking the minors
    as in error until the load method has completed. This avoids the early
    open by simply erroring out the opens with EAGAIN. Obviously we should
    be delaying the open until the load method complete.

    I include the existing patch for completness (it is not really ready for
    merging) to illustrate the issue. I think it is logical that the wait
    should simply be delayed until the load has completed. I am proposing
    to include a wait queue associated with the idr cache for the drm minors
    which we can use to allow open callers to wait_event_interruptible() on.
    I'll be putting together a prototype shortly and will follow up with it.



    Andy Whitcroft (1):
    drm -- stop early access to drm devices

    drivers/gpu/drm/drm_fops.c | 8 ++++++--
    drivers/gpu/drm/drm_pci.c | 4 ++++
    drivers/gpu/drm/drm_platform.c | 4 ++++
    drivers/gpu/drm/drm_stub.c | 2 +-
    4 files changed, 15 insertions(+), 3 deletions(-)


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