Eric Lee / linux-smarc-t335x-v3.2

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Commit b4627321e18582dcbdeb45d77df29d3177107c65

Authored by Vivek Goyal
Committed by Jens Axboe
1 parent 11a691bea4
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

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>

Showing 1 changed file with 13 additions and 3 deletions Side-by-side Diff

... ... @@ -157,6 +157,7 @@
157 157 BE_WORKLOAD = 0,
158 158 RT_WORKLOAD = 1,
159 159 IDLE_WORKLOAD = 2,
  160 + CFQ_PRIO_NR,
160 161 };
161 162  
162 163 /*
163 164  
... ... @@ -181,10 +182,19 @@
181 182 /* number of cfqq currently on this group */
182 183 int nr_cfqq;
183 184  
184   - /* Per group busy queus average. Useful for workload slice calc. */
185   - unsigned int busy_queues_avg[2];
186 185 /*
187   - * rr lists of queues with requests, onle rr for each priority class.
  186 + * Per group busy queus average. Useful for workload slice calc. We
  187 + * create the array for each prio class but at run time it is used
  188 + * only for RT and BE class and slot for IDLE class remains unused.
  189 + * This is primarily done to avoid confusion and a gcc warning.
  190 + */
  191 + unsigned int busy_queues_avg[CFQ_PRIO_NR];
  192 + /*
  193 + * rr lists of queues with requests. We maintain service trees for
  194 + * RT and BE classes. These trees are subdivided in subclasses
  195 + * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
  196 + * class there is no subclassification and all the cfq queues go on
  197 + * a single tree service_tree_idle.
188 198 * Counts are embedded in the cfq_rb_root
189 199 */
190 200 struct cfq_rb_root service_trees[2][3];