On Thu, Feb 14, 2019 at 1:36 AM Bart Van Assche <bvanassche@xxxxxxx> wrote:
>
> On Wed, 2019-02-13 at 12:27 +0800, Ming Lei wrote:
> > On Wed, Feb 13, 2019 at 12:33 AM Theodore Y. Ts'o <tytso@xxxxxxx> wrote:
> > >
> > > Is this a known issue? nvme/012 is triggering the following lockdep warning:
> > >
> > > Thanks,
> > >
> > > - Ted
> > >
> > > [ 1964.751910] run blktests nvme/012 at 2019-02-11 20:58:31
> > > [ 1964.977624] nvmet: adding nsid 1 to subsystem blktests-subsystem-1
> > > [ 1965.006395] nvmet: creating controller 1 for subsystem blktests-subsystem-1 for NQN nqn.2014-08.org.nvmexpress:uuid:8a58b187-6d09-4c5d-bc03-593896d2d80d.
> > > [ 1965.011811] nvme nvme0: ANA group 1: optimized.
> > > [ 1965.011899] nvme nvme0: creating 2 I/O queues.
> > > [ 1965.013966] nvme nvme0: new ctrl: "blktests-subsystem-1"
> > >
> > > [ 1965.282478] ============================================
> > > [ 1965.287922] WARNING: possible recursive locking detected
> > > [ 1965.293364] 5.0.0-rc3-xfstests-00015-g1236f7d60242 #841 Not tainted
> > > [ 1965.299762] --------------------------------------------
> > > [ 1965.305207] ksoftirqd/1/16 is trying to acquire lock:
> > > [ 1965.310389] 000000000282032e (&(&fq->mq_flush_lock)->rlock){..-.}, at: flush_end_io+0x4e/0x1d0
> > > [ 1965.319146]
> > > but task is already holding lock:
> > > [ 1965.325106] 00000000cbadcbc2 (&(&fq->mq_flush_lock)->rlock){..-.}, at: flush_end_io+0x4e/0x1d0
> > > [ 1965.333957]
> > > other info that might help us debug this:
> > > [ 1965.340615] Possible unsafe locking scenario:
> > >
> > > [ 1965.346664] CPU0
> > > [ 1965.349248] ----
> > > [ 1965.351820] lock(&(&fq->mq_flush_lock)->rlock);
> > > [ 1965.356654] lock(&(&fq->mq_flush_lock)->rlock);
> > > [ 1965.361490]
> > > *** DEADLOCK ***
> > >
> > > [ 1965.367541] May be due to missing lock nesting notation
> > >
> > > [ 1965.374636] 1 lock held by ksoftirqd/1/16:
> > > [ 1965.378890] #0: 00000000cbadcbc2 (&(&fq->mq_flush_lock)->rlock){..-.}, at: flush_end_io+0x4e/0x1d0
> > > [ 1965.388080]
> > > stack backtrace:
> > > [ 1965.392570] CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 5.0.0-rc3-xfstests-00015-g1236f7d60242 #841
> > > [ 1965.402002] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > > [ 1965.411411] Call Trace:
> > > [ 1965.413996] dump_stack+0x67/0x90
> > > [ 1965.417433] __lock_acquire.cold.45+0x2b4/0x313
> > > [ 1965.422194] lock_acquire+0x98/0x160
> > > [ 1965.425894] ? flush_end_io+0x4e/0x1d0
> > > [ 1965.429817] _raw_spin_lock_irqsave+0x3b/0x80
> > > [ 1965.434299] ? flush_end_io+0x4e/0x1d0
> > > [ 1965.438162] flush_end_io+0x4e/0x1d0
> > > [ 1965.441909] blk_mq_complete_request+0x76/0x110
> > > [ 1965.446580] nvmet_req_complete+0x15/0x110 [nvmet]
> > > [ 1965.452098] nvmet_bio_done+0x27/0x50 [nvmet]
> > > [ 1965.456634] blk_update_request+0xd7/0x2d0
> > > [ 1965.460869] blk_mq_end_request+0x1a/0x100
> > > [ 1965.465091] blk_flush_complete_seq+0xe5/0x350
> > > [ 1965.469660] flush_end_io+0x12f/0x1d0
> > > [ 1965.473436] blk_done_softirq+0x9f/0xd0
> > > [ 1965.477398] __do_softirq+0xca/0x440
> > > [ 1965.481092] ? smpboot_thread_fn+0x2f/0x1e0
> > > [ 1965.485512] ? smpboot_thread_fn+0x74/0x1e0
> > > [ 1965.489813] ? smpboot_thread_fn+0x118/0x1e0
> > > [ 1965.494379] run_ksoftirqd+0x24/0x50
> > > [ 1965.498081] smpboot_thread_fn+0x113/0x1e0
> > > [ 1965.502399] ? sort_range+0x20/0x20
> > > [ 1965.506008] kthread+0x121/0x140
> > > [ 1965.509395] ? kthread_park+0x80/0x80
> > > [ 1965.513290] ret_from_fork+0x3a/0x50
> > > [ 1965.527032] XFS (nvme0n1): Mounting V5 Filesystem
> > > [ 1965.541778] XFS (nvme0n1): Ending clean mount
> > > [ 2064.142830] XFS (nvme0n1): Unmounting Filesystem
> > > [ 2064.171432] nvme nvme0: Removing ctrl: NQN "blktests-subsystem-1"
> >
> > That is a false positive.
> >
> > It is caused by calling host request's completion handler from target
> > IO's completion
> > handler directly, and this way should be nvme-loop only.
> >
> > We may need to annotate the locks in .end_io of blk-flush for avoiding
> > this warning.
> >
> > BTW, this way of nvme-loop handling IO completion may trigger soft lockup too.
>
> Hi Ming,
>
> Can you clarify that last statement?
I mean it is easy to trigger soft lockup by the way of nested IO
completion, given
all are done in irq context.
>
> You may want to know that the patch below suppresses this lockdep complaint. I will
> include it in my "dynamic lockdep key" patch series.
>
>
> [PATCH] block: Suppress a false positive lockdep complaint
>
> Avoid that running test nvme/012 from the blktests suite triggers the
> following lockdep complaint:
>
> ============================================
> WARNING: possible recursive locking detected
> 5.0.0-rc3-xfstests-00015-g1236f7d60242 #841 Not tainted
> --------------------------------------------
> ksoftirqd/1/16 is trying to acquire lock:
> 000000000282032e (&(&fq->mq_flush_lock)->rlock){..-.}, at: flush_end_io+0x4e/0x1d0
>
> but task is already holding lock:
> 00000000cbadcbc2 (&(&fq->mq_flush_lock)->rlock){..-.}, at: flush_end_io+0x4e/0x1d0
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(&(&fq->mq_flush_lock)->rlock);
> lock(&(&fq->mq_flush_lock)->rlock);
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 1 lock held by ksoftirqd/1/16:
> #0: 00000000cbadcbc2 (&(&fq->mq_flush_lock)->rlock){..-.}, at: flush_end_io+0x4e/0x1d0
>
> stack backtrace:
> CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 5.0.0-rc3-xfstests-00015-g1236f7d60242 #841
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> dump_stack+0x67/0x90
> __lock_acquire.cold.45+0x2b4/0x313
> lock_acquire+0x98/0x160
> _raw_spin_lock_irqsave+0x3b/0x80
> flush_end_io+0x4e/0x1d0
> blk_mq_complete_request+0x76/0x110
> nvmet_req_complete+0x15/0x110 [nvmet]
> nvmet_bio_done+0x27/0x50 [nvmet]
> blk_update_request+0xd7/0x2d0
> blk_mq_end_request+0x1a/0x100
> blk_flush_complete_seq+0xe5/0x350
> flush_end_io+0x12f/0x1d0
> blk_done_softirq+0x9f/0xd0
> __do_softirq+0xca/0x440
> run_ksoftirqd+0x24/0x50
> smpboot_thread_fn+0x113/0x1e0
> kthread+0x121/0x140
> ret_from_fork+0x3a/0x50
>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/blk-flush.c | 4 +++-
> block/blk.h | 1 +
> 2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-flush.c b/block/blk-flush.c
> index 6e0f2d97fc6d..c4fa6dd73664 100644
> --- a/block/blk-flush.c
> +++ b/block/blk-flush.c
> @@ -472,7 +472,8 @@ struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
> if (!fq)
> goto fail;
>
> - spin_lock_init(&fq->mq_flush_lock);
> + lockdep_register_key(&fq->key);
> + spin_lock_init_key(&fq->mq_flush_lock, &fq->key);
>
> rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
> fq->flush_rq = kzalloc_node(rq_sz, flags, node);
> @@ -497,6 +498,7 @@ void blk_free_flush_queue(struct blk_flush_queue *fq)
> if (!fq)
> return;
>
> + lockdep_unregister_key(&fq->key);
> kfree(fq->flush_rq);
> kfree(fq);
> }
> diff --git a/block/blk.h b/block/blk.h
> index 848278c52030..10f5e19aa4a1 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -28,6 +28,7 @@ struct blk_flush_queue {
> * at the same time
> */
> struct request *orig_rq;
> + struct lock_class_key key;
> spinlock_t mq_flush_lock;
> };
For this particular issue, seems it is over-kill to use per_flush_queue key,
and it should have been enough to use one independent class key for
nvme-loop's flush queue.
Thanks,
Ming Lei
