tree 2f723e1b69ab08e12528f677f04edbfc7473b7c5
parent 4263a2f1dad8c8e7ce2352a0cbc882c2b0c044a9
author NeilBrown <neilb@suse.de> 1302523990 +0200
committer Jens Axboe <jaxboe@fusionio.com> 1302523990 +0200

block: splice plug list to local context

If the request_fn ends up blocking, we could be re-entering
the plug flush. Since the list is protected by explicitly
not allowing schedule events, this isn't a terribly good idea.

Additionally, it can cause us to recurse. As request_fn called by
__blk_run_queue is allowed to 'schedule()' (after dropping the queue
lock of course), it is possible to get a recursive call:

 schedule -> blk_flush_plug -> __blk_finish_plug -> flush_plug_list
      -> __blk_run_queue -> request_fn -> schedule

We must make sure that the second schedule does not call into
blk_flush_plug again.  So instead of leaving the list of requests on
blk_plug->list, move them to a separate list leaving blk_plug->list
empty.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>