cfq-iosched: Fix a gcc 4.5 warning and put some comments
authorVivek Goyal <vgoyal@redhat.com>
Fri, 22 Oct 2010 07:48:43 +0000 (09:48 +0200)
committerJens Axboe <jaxboe@fusionio.com>
Fri, 22 Oct 2010 07:48:43 +0000 (09:48 +0200)
commitb4627321e18582dcbdeb45d77df29d3177107c65
treef494dae7f39f219d73aa9752dfd3844293d65f50
parent11a691bea48887c27425cc40bf291e74c922df25
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>
block/cfq-iosched.c