blk-mq: fix panic during blk_mq_run_work_fn()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I58VDJ
CVE: NA

--------------------------------

Our test report a following crash:

BUG: kernel NULL pointer dereference, address: 0000000000000018
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 6 PID: 265 Comm: kworker/6:1H Kdump: loaded Tainted: G           O      5.10.0-60.17.0.h43.eulerosv2r11.x86_64 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-20220320_160524-szxrtosci10000 04/01/2014
Workqueue: kblockd blk_mq_run_work_fn
RIP: 0010:blk_mq_delay_run_hw_queues+0xb6/0xe0
RSP: 0018:ffffacc6803d3d88 EFLAGS: 00010246
RAX: 0000000000000006 RBX: ffff99e2c3d25008 RCX: 00000000ffffffff
RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff99e2c911ae18
RBP: ffffacc6803d3dd8 R08: 0000000000000000 R09: ffff99e2c0901f6c
R10: 0000000000000018 R11: 0000000000000018 R12: ffff99e2c911ae18
R13: 0000000000000000 R14: 0000000000000003 R15: ffff99e2c911ae18
FS:  0000000000000000(0000) GS:ffff99e6bbf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 000000007460a006 CR4: 00000000003706e0
Call Trace:
 __blk_mq_do_dispatch_sched+0x2a7/0x2c0
 ? newidle_balance+0x23e/0x2f0
 __blk_mq_sched_dispatch_requests+0x13f/0x190
 blk_mq_sched_dispatch_requests+0x30/0x60
 __blk_mq_run_hw_queue+0x47/0xd0
 process_one_work+0x1b0/0x350
 worker_thread+0x49/0x300
 ? rescuer_thread+0x3a0/0x3a0
 kthread+0xfe/0x140
 ? kthread_park+0x90/0x90
 ret_from_fork+0x22/0x30

After digging from vmcore, I found that the queue is cleaned
up(blk_cleanup_queue() is done) and tag set is
freed(blk_mq_free_tag_set() is done).

There are two problems here:

1) blk_mq_delay_run_hw_queues() will only be called from
__blk_mq_do_dispatch_sched() if e->type->ops.has_work() return true.
This seems impossible because blk_cleanup_queue() is done, and there
should be no io. However, bfq_has_work() can return true even if no
io is queued. This is because bfq_has_work() is using busy queues, and
bfq_queue can stay busy after dispatching all the requests.

2) 'hctx->run_work' still exists after blk_cleanup_queue().
blk_mq_cancel_work_sync() is called from blk_cleanup_queue() to cancel
all the 'run_work'. However, there is no guarantee that new 'run_work'
won't be queued after that(and before blk_mq_exit_queue() is done).

The first problem is not the root cause, this patch just fix the second
problem by grabbing 'q_usage_counter' before queuing 'hctx->run_work'.
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

block/blk-mq.c

@@ -1627,8 +1627,16 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 		put_cpu();
 	}
 
+	/*
+	 * No need to queue work if there is no io, and this can avoid race
+	 * with blk_cleanup_queue().
+	 */
+	if (!percpu_ref_tryget(&hctx->queue->q_usage_counter))
+		return;
+
 	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
 				    msecs_to_jiffies(msecs));
+	percpu_ref_put(&hctx->queue->q_usage_counter);
 }
 
 /**