[PATCH] cfq-iosched: fix crash in do_div()

We don't clear the seek stat values in cfq_alloc_io_context(), and if
->seek_mean is unlucky enough to be set to -36 by chance, the first
invocation of cfq_update_io_seektime() will oops with a divide by zero
in do_div().

Just memset the entire cic instead of filling invididual values
independently.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

block/cfq-iosched.c

@@ -1323,17 +1323,12 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
 	struct cfq_io_context *cic = kmem_cache_alloc(cfq_ioc_pool, gfp_mask);
 
 	if (cic) {
-		RB_CLEAR(&cic->rb_node);
-		cic->key = NULL;
-		cic->cfqq[ASYNC] = NULL;
-		cic->cfqq[SYNC] = NULL;
+		memset(cic, 0, sizeof(*cic));
+		RB_CLEAR_COLOR(&cic->rb_node);
 		cic->last_end_request = jiffies;
-		cic->ttime_total = 0;
-		cic->ttime_samples = 0;
-		cic->ttime_mean = 0;
+		INIT_LIST_HEAD(&cic->queue_list);
 		cic->dtor = cfq_free_io_context;
 		cic->exit = cfq_exit_io_context;
-		INIT_LIST_HEAD(&cic->queue_list);
 		atomic_inc(&ioc_count);
 	}