[PATCH -next v2] blk-mq: fix panic during blk_mq_run_work_fn()

[Yu Kuai <yukuai3@huawei.com>]

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. Commit ddc25c86b466 ("block, bfq: make bfq_has_work()
more accurate") fix the problem in bfq. And currently ohter schedulers
don't have such problem.

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, it will only increase the
probability of the second problem. this patch fix the second problem by
checking the 'QUEUE_FLAG_DEAD' before queuing 'hctx->run_work', and
using 'queue_lock' to synchronize queuing new work and cacelling the
old work.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-core.c |  3 +++
 block/blk-mq.c   | 10 ++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 80fa73c419a9..f3e36d8143ec 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -314,7 +314,10 @@ void blk_cleanup_queue(struct request_queue *q)
 	 */
 	blk_freeze_queue(q);
 
+	/* New 'hctx->run_work' can't be queued after setting the dead flag */
+	spin_lock_irq(&q->queue_lock);
 	blk_queue_flag_set(QUEUE_FLAG_DEAD, q);
+	spin_unlock_irq(&q->queue_lock);
 
 	blk_sync_queue(q);
 	if (queue_is_mq(q)) {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ed1869a305c4..fb35d335d554 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2093,6 +2093,8 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
 static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 					unsigned long msecs)
 {
+	unsigned long flags;
+
 	if (unlikely(blk_mq_hctx_stopped(hctx)))
 		return;
 
@@ -2107,8 +2109,12 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 		put_cpu();
 	}
 
-	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
-				    msecs_to_jiffies(msecs));
+	spin_lock_irqsave(&hctx->queue->queue_lock, flags);
+	if (!blk_queue_dead(hctx->queue))
+		kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
+					    &hctx->run_work,
+					    msecs_to_jiffies(msecs));
+	spin_unlock_irqrestore(&hctx->queue->queue_lock, flags);
 }
 
 /**
-- 
2.31.1