Commit b4627321 authored Oct 22, 2010 by Vivek Goyal Committed by Jens Axboe Oct 22, 2010

cfq-iosched: Fix a gcc 4.5 warning and put some comments



- Andi encountedred following warning with gcc 4.5

  linux/block/cfq-iosched.c: In function ‘cfq_dispatch_requests’:
  linux/block/cfq-iosched.c:2156:3: warning: array subscript is above array
  bounds

- Warning happens due to following code.

  slice = group_slice * count /
		max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio],
		cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg));

  gcc is complaining about cfqg->busy_queues_avg[] being indexed by CFQ
  prio classes (RT, BE and IDLE) while the array size is only 2.

- At run time, we never access cfqg->busy_queues_avg[IDLE] and return from
  function before this code hits.

- To fix warning increase the array size though it will remain unused. This
  patch also puts some comments to clarify some of the confusions.

- I have taken Jens's patch and modified it a bit.

- Compile tested with gcc 4.4 and boot tested. I don't have gcc 4.5
  running, Andi can you please test it with gcc 4.5 to make sure it
  worked.

Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

parent 11a691be

block/cfq-iosched.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -157,6 +157,7 @@ enum wl_prio_t {
		BE_WORKLOAD = 0,
		RT_WORKLOAD = 1,
		IDLE_WORKLOAD = 2,
		CFQ_PRIO_NR,
		};

		/*
		@@ -181,10 +182,19 @@ struct cfq_group {
		/* number of cfqq currently on this group */
		int nr_cfqq;

		/* Per group busy queus average. Useful for workload slice calc. */
		unsigned int busy_queues_avg[2];
		/*
		* rr lists of queues with requests, onle rr for each priority class.
		* Per group busy queus average. Useful for workload slice calc. We
		* create the array for each prio class but at run time it is used
		* only for RT and BE class and slot for IDLE class remains unused.
		* This is primarily done to avoid confusion and a gcc warning.
		*/
		unsigned int busy_queues_avg[CFQ_PRIO_NR];
		/*
		* rr lists of queues with requests. We maintain service trees for
		* RT and BE classes. These trees are subdivided in subclasses
		* of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
		* class there is no subclassification and all the cfq queues go on
		* a single tree service_tree_idle.
		* Counts are embedded in the cfq_rb_root
		*/
		struct cfq_rb_root service_trees[2][3];

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