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 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@xxxxxxxxxx>
---
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 c3f1e46ddd43..2609805861be 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -318,7 +318,10 @@ void blk_cleanup_queue(struct request_queue *q)
/* cleanup rq qos structures for queue without disk */
rq_qos_exit(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 2cf011b57cf9..34b4914204dd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2042,6 +2042,8 @@ 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 flag;
+
if (unlikely(blk_mq_hctx_stopped(hctx)))
return;
@@ -2056,8 +2058,12 @@ 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, flag);
+ 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, flag);
}
/**
--
2.31.1
