commit
255bb490c8c27eed484d538efe6ef6a7473bd3f6 upstream.
blk-flush decomposes a flush into sequence of multiple requests. On
completion of a request, the next one is queued; however, block layer
must not implicitly call into q->request_fn() directly from completion
path. This makes the queue behave unexpectedly when seen from the
drivers and violates the assumption that q->request_fn() is called
with process context + queue_lock.
This patch makes blk-flush the following two changes to make sure
q->request_fn() is not called directly from request completion path.
- blk_flush_complete_seq_end_io() now asks __blk_run_queue() to always
use kblockd instead of calling directly into q->request_fn().
- queue_next_fseq() uses ELEVATOR_INSERT_REQUEUE instead of
ELEVATOR_INSERT_FRONT so that elv_insert() doesn't try to unplug the
request queue directly.
Reported by Jan in the following threads.
http://thread.gmane.org/gmane.linux.ide/48778
http://thread.gmane.org/gmane.linux.ide/48786
stable: applicable to v2.6.37.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jan Beulich <JBeulich@novell.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
/*
* Moving a request silently to empty queue_head may stall the
- * queue. Kick the queue in those cases.
+ * queue. Kick the queue in those cases. This function is called
+ * from request completion path and calling directly into
+ * request_fn may confuse the driver. Always use kblockd.
*/
if (was_empty && next_rq)
- __blk_run_queue(q, false);
+ __blk_run_queue(q, true);
}
static void pre_flush_end_io(struct request *rq, int error)
BUG();
}
- elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+ elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
return rq;
}