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  1. 11 May, 2011 2 commits
    • NeilBrown's avatar
      md: reject a re-add request that cannot be honoured. · bedd86b7
      NeilBrown authored 
      The 'add_new_disk' ioctl can be used to add a device either as a
spare, or as an active disk that just needs to be resynced based on
write-intent-bitmap information (re-add)

Currently if a re-add is requested but fails we add as a spare
instead.  This makes it impossible for user-space to check for
failure.

So change to require that a re-add attempt will either succeed or
completely fail.  User-space can then decide what to do next.
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
      bedd86b7
    • NeilBrown's avatar
      md: Fix race when creating a new md device. · b0140891
      NeilBrown authored 
      There is a race when creating an md device by opening /dev/mdXX.

If two processes do this at much the same time they will follow the
call path
  __blkdev_get -> get_gendisk -> kobj_lookup

The first will call
  -> md_probe -> md_alloc -> add_disk -> blk_register_region

and the race happens when the second gets to kobj_lookup after
add_disk has called blk_register_region but before it returns to
md_alloc.

In the case the second will not call md_probe (as the probe is already
done) but will get a handle on the gendisk, return to __blkdev_get
which will then call md_open (via the ->open) pointer.

As mddev->gendisk hasn't been set yet, md_open will think something is
wrong an return with ERESTARTSYS.

This can loop endlessly while the first thread makes no progress
through add_disk.  Nothing is blocking it, but due to scheduler
behaviour it doesn't get a turn.
So this is essentially a live-lock.

We fix this by simply moving the assignment to mddev->gendisk before
the call the add_disk() so md_open doesn't get confused.
Also move blk_queue_flush earlier because add_disk should be as late
as possible.

To make sure that md_open doesn't complete until md_alloc has done all
that is needed, we take mddev->open_mutex during the last part of
md_alloc.  md_open will wait for this.

This can cause a lock-up on boot so Cc:ing for stable.
For 2.6.36 and earlier a different patch will be needed as the
'blk_queue_flush' call isn't there.
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Reported-by: default avatarThomas Jarosch <thomas.jarosch@intra2net.com>
Tested-by: default avatarThomas Jarosch <thomas.jarosch@intra2net.com>
Cc: stable@kernel.org
      b0140891
  3. 10 May, 2011 2 commits
  5. 09 May, 2011 27 commits
  7. 08 May, 2011 6 commits
  9. 07 May, 2011 2 commits
  11. 06 May, 2011 1 commit
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