Hi Jan,

I love your patch! Yet something to improve:

[auto build test ERROR on axboe-block/for-next]
[also build test ERROR on v5.16-rc3 next-20211201]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Jan-Kara/bfq-Fix-use-after-free-with-cgroups/20211201-213549
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: um-i386_defconfig (https://download.01.org/0day-ci/archive/20211202/202112020023.Klrg0J1F-lkp@intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/2154a2da8d69308aca6bb431da2d4d9e3e687daa
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Jan-Kara/bfq-Fix-use-after-free-with-cgroups/20211201-213549
        git checkout 2154a2da8d69308aca6bb431da2d4d9e3e687daa
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 O=build_dir ARCH=um SUBARCH=i386 SHELL=/bin/bash block/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>

All errors (new ones prefixed by >>):

   block/bfq-iosched.c: In function 'bfq_init_bfqq':

quoted

block/bfq-iosched.c:5472:44: error: 'struct bfq_group' has no member named 'children'

    5472 |  hlist_add_head(&bfqq->children_node, &bfqg->children);
         |                                            ^~


vim +5472 block/bfq-iosched.c

  5460	
  5461	static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_group *bfqg,
  5462				  struct bfq_queue *bfqq, struct bfq_io_cq *bic,
  5463				  pid_t pid, int is_sync)
  5464	{
  5465		u64 now_ns = ktime_get_ns();
  5466	
  5467		RB_CLEAR_NODE(&bfqq->entity.rb_node);
  5468		INIT_LIST_HEAD(&bfqq->fifo);
  5469		INIT_HLIST_NODE(&bfqq->burst_list_node);
  5470		INIT_HLIST_NODE(&bfqq->woken_list_node);
  5471		INIT_HLIST_HEAD(&bfqq->woken_list);

5472		hlist_add_head(&bfqq->children_node, &bfqg->children);

  5473	
  5474		bfqq->ref = 0;
  5475		bfqq->bfqd = bfqd;
  5476	
  5477		if (bic)
  5478			bfq_set_next_ioprio_data(bfqq, bic);
  5479	
  5480		if (is_sync) {
  5481			/*
  5482			 * No need to mark as has_short_ttime if in
  5483			 * idle_class, because no device idling is performed
  5484			 * for queues in idle class
  5485			 */
  5486			if (!bfq_class_idle(bfqq))
  5487				/* tentatively mark as has_short_ttime */
  5488				bfq_mark_bfqq_has_short_ttime(bfqq);
  5489			bfq_mark_bfqq_sync(bfqq);
  5490			bfq_mark_bfqq_just_created(bfqq);
  5491		} else
  5492			bfq_clear_bfqq_sync(bfqq);
  5493	
  5494		/* set end request to minus infinity from now */
  5495		bfqq->ttime.last_end_request = now_ns + 1;
  5496	
  5497		bfqq->creation_time = jiffies;
  5498	
  5499		bfqq->io_start_time = now_ns;
  5500	
  5501		bfq_mark_bfqq_IO_bound(bfqq);
  5502	
  5503		bfqq->pid = pid;
  5504	
  5505		/* Tentative initial value to trade off between thr and lat */
  5506		bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
  5507		bfqq->budget_timeout = bfq_smallest_from_now();
  5508	
  5509		bfqq->wr_coeff = 1;
  5510		bfqq->last_wr_start_finish = jiffies;
  5511		bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
  5512		bfqq->split_time = bfq_smallest_from_now();
  5513	
  5514		/*
  5515		 * To not forget the possibly high bandwidth consumed by a
  5516		 * process/queue in the recent past,
  5517		 * bfq_bfqq_softrt_next_start() returns a value at least equal
  5518		 * to the current value of bfqq->soft_rt_next_start (see
  5519		 * comments on bfq_bfqq_softrt_next_start).  Set
  5520		 * soft_rt_next_start to now, to mean that bfqq has consumed
  5521		 * no bandwidth so far.
  5522		 */
  5523		bfqq->soft_rt_next_start = jiffies;
  5524	
  5525		/* first request is almost certainly seeky */
  5526		bfqq->seek_history = 1;
  5527	}
  5528	

---
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