Parallel hotplugging event issues

[Sjoerd Simons]

Hi,

  Attached is a patch to fix some basic issues with the parallel event
  processing. The patch description has some more detailed information.

  Unfortunately after this fix more issues show up. One specific issue i'm
  seeing is that when pulling out my usb stick, the force unmounting fails to
  work. Some analysis shows the issue is the following.

  The device tree looks something like this
    *- A: scsi host device
     *- B: block device (full device)
      *- C: block device (one partition on the device

  When the usb device is pulled out removal events are received for all these
  devices. The event dependency code properly detects that the full device
  block device depends on the leaf block device. But not the relation between
  the scsi_host and the block devices. So the event for A and C is handled in
  parallel.

  Now when a device is removed, all it's child devices get removed too.. So the
  event for A removes device C, causing the handlers of C to get confused (as C
  is gone).. What this shows is that purely using the sysfs path prefixes for
  dependency information isn't enough, the relationship of devices as hal has
  detected them needs to be taken into account too.

  Personally i'm not sure if it would be good to have the parallel event
  processing in the next release. It might be better to back it out for now,
  get the release out. And merge it afterwards, so that there is some more time
  to work out all the issues with parallelizing these things. I'm afraid it
  will keep triggering a lot of little issues for a while.

  Sjoerd
-- 
Normal times may possibly be over forever.
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