Re: [PATCH] block: fix lock dependency between percpu alloc lock and elevator lock

[kernel test robot <lkp@intel.com>]

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
In-Reply-To: <20250520103425.1259712-1-nilay@linux.ibm.com>
References: <20250520103425.1259712-1-nilay@linux.ibm.com>
TO: Nilay Shroff <nilay@linux.ibm.com>
TO: linux-block@vger.kernel.org
CC: ming.lei@redhat.com
CC: hch@lst.de
CC: axboe@kernel.dk
CC: sth@linux.ibm.com
CC: gjoyce@ibm.com

Hi Nilay,

kernel test robot noticed the following build warnings:

[auto build test WARNING on axboe-block/for-next]
[also build test WARNING on next-20250516]
[cannot apply to linus/master v6.15-rc7]
[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#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Nilay-Shroff/block-fix-lock-dependency-between-percpu-alloc-lock-and-elevator-lock/20250520-183641
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/20250520103425.1259712-1-nilay%40linux.ibm.com
patch subject: [PATCH] block: fix lock dependency between percpu alloc lock and elevator lock
:::::: branch date: 17 hours ago
:::::: commit date: 17 hours ago
config: powerpc64-randconfig-r072-20250521 (https://download.01.org/0day-ci/archive/20250521/202505211110.xlMp4URV-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <error27@gmail.com>
| Closes: https://lore.kernel.org/r/202505211110.xlMp4URV-lkp@intel.com/

New smatch warnings:
block/blk-mq-sched.c:406 blk_mq_sched_tags_release() warn: iterator 'i' not incremented
block/blk-mq-sched.c:611 blk_mq_sched_copy_tags() warn: iterator 'i' not incremented

Old smatch warnings:
block/blk-mq-sched.c:434 blk_mq_sched_reg_debugfs() warn: iterator 'i' not incremented
block/blk-mq-sched.c:445 blk_mq_sched_unreg_debugfs() warn: iterator 'i' not incremented
block/blk-mq-sched.c:572 blk_mq_init_sched() warn: iterator 'i' not incremented
block/blk-mq-sched.c:621 blk_mq_exit_sched() warn: iterator 'i' not incremented

vim +/i +406 block/blk-mq-sched.c

bd166ef183c263 Jens Axboe   2017-01-17  395  
cc96aa538d1d8f Nilay Shroff 2025-05-20  396  /*
cc96aa538d1d8f Nilay Shroff 2025-05-20  397   * Called in queue's release handler, tagset has gone away. Sched tags
cc96aa538d1d8f Nilay Shroff 2025-05-20  398   * are freed later when we finish switching the elevator and release
cc96aa538d1d8f Nilay Shroff 2025-05-20  399   * the ->elevator_lock and ->frezze_lock.
cc96aa538d1d8f Nilay Shroff 2025-05-20  400   */
cc96aa538d1d8f Nilay Shroff 2025-05-20  401  static void blk_mq_sched_tags_release(struct request_queue *q, unsigned int flags)
bd166ef183c263 Jens Axboe   2017-01-17  402  {
bd166ef183c263 Jens Axboe   2017-01-17  403  	struct blk_mq_hw_ctx *hctx;
4f481208749a22 Ming Lei     2022-03-08  404  	unsigned long i;
bd166ef183c263 Jens Axboe   2017-01-17  405  
cc96aa538d1d8f Nilay Shroff 2025-05-20 @406  	queue_for_each_hw_ctx(q, hctx, i)
c3e2219216c929 Ming Lei     2019-06-04  407  		hctx->sched_tags = NULL;
e155b0c238b20f John Garry   2021-10-05  408  
079a2e3e862548 John Garry   2021-10-05  409  	if (blk_mq_is_shared_tags(flags))
cc96aa538d1d8f Nilay Shroff 2025-05-20  410  		q->sched_shared_tags = NULL;
bd166ef183c263 Jens Axboe   2017-01-17  411  }
cc96aa538d1d8f Nilay Shroff 2025-05-20  412  static int blk_mq_init_sched_shared_tags(struct request_queue *queue,
cc96aa538d1d8f Nilay Shroff 2025-05-20  413  		struct elv_data *elv)
d97e594c51660b John Garry   2021-05-13  414  {
d97e594c51660b John Garry   2021-05-13  415  	/*
cc96aa538d1d8f Nilay Shroff 2025-05-20  416  	 * We allocated the sched shared tags before initiating the elevator
cc96aa538d1d8f Nilay Shroff 2025-05-20  417  	 * switch, prior to acquiring ->elevator_lock and ->freeze_lock, and
cc96aa538d1d8f Nilay Shroff 2025-05-20  418  	 * stored them in the elevator context. So assign those pre-allocated
cc96aa538d1d8f Nilay Shroff 2025-05-20  419  	 * tags now.
d97e594c51660b John Garry   2021-05-13  420  	 */
cc96aa538d1d8f Nilay Shroff 2025-05-20  421  	queue->sched_shared_tags = elv->shared_tags;
079a2e3e862548 John Garry   2021-10-05  422  	blk_mq_tag_update_sched_shared_tags(queue);
d97e594c51660b John Garry   2021-05-13  423  
d97e594c51660b John Garry   2021-05-13  424  	return 0;
d97e594c51660b John Garry   2021-05-13  425  }
d97e594c51660b John Garry   2021-05-13  426  

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