tree 933aa0ca3bffef5b1457c516fbe3e8690b4c4cb1
parent af1f951eb6ef27b01cbfb3f6c21b770af4368a6d
author Dan Williams <dan.j.williams@intel.com> 1247599142 -0700
committer Dan Williams <dan.j.williams@intel.com> 1251598167 -0700

async_tx: remove walk of tx->parent chain in dma_wait_for_async_tx

We currently walk the parent chain when waiting for a given tx to
complete however this walk may race with the driver cleanup routine.
The routines in async_raid6_recov.c may fall back to the synchronous
path at any point so we need to be prepared to call async_tx_quiesce()
(which calls  dma_wait_for_async_tx).  To remove the ->parent walk we
guarantee that every time a dependency is attached ->issue_pending() is
invoked, then we can simply poll the initial descriptor until
completion.

This also allows for a lighter weight 'issue pending' implementation as
there is no longer a requirement to iterate through all the channels'
->issue_pending() routines as long as operations have been submitted in
an ordered chain.  async_tx_issue_pending() is added for this case.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>