tree 2f148dd8e82b287fc7b682cabc5614e3046d8949
parent 280d45f6c35d8d7a0fe20c36caf426e3ac139cf9
author Christoph Hellwig <hch@lst.de> 1382988838 -0600
committer Jens Axboe <axboe@kernel.dk> 1382988838 -0600

blk-mq: fix for flush deadlock

The flush state machine takes in a struct request, which then is
submitted multiple times to the underling driver.  The old block code
requeses the same request for each of those, so it does not have an
issue with tapping into the request pool.  The new one on the other hand
allocates a new request for each of the actualy steps of the flush
sequence. If have already allocated all of the tags for IO, we will
fail allocating the flush request.

Set aside a reserved request just for flushes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>