1. Aug 22, 2012
    • Dave Airlie's avatar
      fbcon: fix race condition between console lock and cursor timer · ec5da7f8
      Dave Airlie authored
      
      
      So we've had a fair few reports of fbcon handover breakage between
      efi/vesafb and i915 surface recently, so I dedicated a couple of
      days to finding the problem.
      
      Essentially the last thing we saw was the conflicting framebuffer
      message and that was all.
      
      So after much tracing with direct netconsole writes (printks
      under console_lock not so useful), I think I found the race.
      
        Thread A (driver load)    Thread B (timer thread)
          unbind_con_driver ->              |
          bind_con_driver ->                |
          vc->vc_sw->con_deinit ->          |
          fbcon_deinit ->                   |
          console_lock()                    |
              |                             |
              |                       fbcon_flashcursor timer fires
              |                       console_lock() <- blocked for A
              |
              |
        fbcon_del_cursor_timer ->
          del_timer_sync
          (BOOM)
      
      Of course because all of this is under the console lock,
      we never see anything, also since we also just unbound the active
      console guess what we never see anything.
      
      Hopefully this fixes the problem for anyone seeing vesafb->kms
      driver handoff.
      
      Signed-off-by: default avatarDavid Airlie <airlied@redhat.com>
      Acked-by: default avatarAlan Cox <alan@lxorguk.ukuu.org.uk>
      Cc: stable@vger.kernel.org
      Tested-by: default avatarJosh Boyer <jwboyer@gmail.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      ec5da7f8
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