Commit db3b5848 authored Jun 17, 2005 by Kiyoshi Ueda Committed by Jens Axboe Jun 17, 2005

When cfq I/O scheduler is selected, get_request() in __make_request() calls


__cfq_get_queue().  __cfq_get_queue() finds an existing queue (struct
cfq_queue) of the current process for the device and returns it.  If it's not
found, __cfq_get_queue() creates and returns a new one if __cfq_get_queue() is
called with __GFP_WAIT flag, or __cfq_get_queue() returns NULL (this means that
get_request() fails) if no __GFP_WAIT flag.

On the other hand, in __make_request(), get_request() is called without
__GFP_WAIT flag at the first time.  Thus, the get_request() fails when there is
no existing queue, typically when it's called for the first I/O request of the
process to the device.

Though it will be followed by get_request_wait() for general case,
__make_request() will just end the I/O with an error (EWOULDBLOCK) when the
request was for read-ahead.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

parent c374f127

drivers/block/cfq-iosched.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -1202,14 +1202,17 @@ __cfq_get_queue(struct cfq_data *cfqd, unsigned long key, int gfp_mask)
		if (new_cfqq) {
		cfqq = new_cfqq;
		new_cfqq = NULL;
		} else if (gfp_mask & __GFP_WAIT) {
		} else {
		spin_unlock_irq(cfqd->queue->queue_lock);
		new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
		spin_lock_irq(cfqd->queue->queue_lock);
		goto retry;
		} else

		if (!new_cfqq && !(gfp_mask & __GFP_WAIT))
		goto out;

		goto retry;
		}

		memset(cfqq, 0, sizeof(*cfqq));

		INIT_HLIST_NODE(&cfqq->cfq_hash);