blk_mq_sched_insert_request: inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage

[Michael Ellerman <mpe@ellerman.id.au>]

Hi Jens,

I'm seeing the lockdep warning below on shutdown on a Power8 machine
using IPR.

If I'm reading it right it looks like the spin_lock() (non-irq) in
blk_mq_sched_insert_request() is the immediate cause.

Looking at blk_mq_requeue_work() (the caller), it is doing
spin_lock_irqsave(). So is switching blk_mq_sched_insert_request() to
spin_lock_irqsave() the right fix?

cheers


ipr 0001:08:00.0: shutdown

================================
WARNING: inconsistent lock state
4.13.0-rc2-gcc6x-gf74c89b #1 Not tainted
--------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
swapper/28/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
 (&(&hctx->lock)->rlock){+.?...}, at: [<c0000000005b60f4>] blk_mq_sched_dispatch_requests+0xa4/0x2a0
{SOFTIRQ-ON-W} state was registered at:
  lock_acquire+0xec/0x2e0
  _raw_spin_lock+0x44/0x70
  blk_mq_sched_insert_request+0x88/0x1f0
  blk_mq_requeue_work+0x108/0x180
  process_one_work+0x310/0x800
  worker_thread+0x88/0x520
  kthread+0x164/0x1b0
  ret_from_kernel_thread+0x5c/0x74
irq event stamp: 3572314
hardirqs last  enabled at (3572314): [<c000000000b71998>] _raw_spin_unlock_irqrestore+0x58/0xb0
hardirqs last disabled at (3572313): [<c000000000b716ec>] _raw_spin_lock_irqsave+0x3c/0x90
softirqs last  enabled at (3572302): [<c0000000000df17c>] irq_enter+0x9c/0xe0
softirqs last disabled at (3572303): [<c0000000000df2c8>] irq_exit+0x108/0x150

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&hctx->lock)->rlock);
  <Interrupt>
    lock(&(&hctx->lock)->rlock);

 *** DEADLOCK ***

2 locks held by swapper/28/0:
 #0:  ((&ipr_cmd->timer)){+.-...}, at: [<c0000000001936f0>] call_timer_fn+0x10/0x4b0
 #1:  (rcu_read_lock){......}, at: [<c0000000005aca60>] __blk_mq_run_hw_queue+0xa0/0x2c0

stack backtrace:
CPU: 28 PID: 0 Comm: swapper/28 Not tainted 4.13.0-rc2-gcc6x-gf74c89b #1
Call Trace:
[c000001fffe97550] [c000000000b50818] dump_stack+0xe8/0x160 (unreliable)
[c000001fffe97590] [c0000000001586d0] print_usage_bug+0x2d0/0x390
[c000001fffe97640] [c000000000158f34] mark_lock+0x7a4/0x8e0
[c000001fffe976f0] [c00000000015a000] __lock_acquire+0x6a0/0x1a70
[c000001fffe97860] [c00000000015befc] lock_acquire+0xec/0x2e0
[c000001fffe97930] [c000000000b71514] _raw_spin_lock+0x44/0x70
[c000001fffe97960] [c0000000005b60f4] blk_mq_sched_dispatch_requests+0xa4/0x2a0
[c000001fffe979c0] [c0000000005acac0] __blk_mq_run_hw_queue+0x100/0x2c0
[c000001fffe97a00] [c0000000005ad478] __blk_mq_delay_run_hw_queue+0x118/0x130
[c000001fffe97a40] [c0000000005ad61c] blk_mq_start_hw_queues+0x6c/0xa0
[c000001fffe97a80] [c000000000797aac] scsi_kick_queue+0x2c/0x60
[c000001fffe97aa0] [c000000000797cf0] scsi_run_queue+0x210/0x360
[c000001fffe97b10] [c00000000079b888] scsi_run_host_queues+0x48/0x80
[c000001fffe97b40] [c0000000007b6090] ipr_ioa_bringdown_done+0x70/0x1e0
[c000001fffe97bc0] [c0000000007bc860] ipr_reset_ioa_job+0x80/0xf0
[c000001fffe97bf0] [c0000000007b4d50] ipr_reset_timer_done+0xd0/0x100
[c000001fffe97c30] [c0000000001937bc] call_timer_fn+0xdc/0x4b0
[c000001fffe97cf0] [c000000000193d08] expire_timers+0x178/0x330
[c000001fffe97d60] [c0000000001940c8] run_timer_softirq+0xb8/0x120
[c000001fffe97de0] [c000000000b726a8] __do_softirq+0x168/0x6d8
[c000001fffe97ef0] [c0000000000df2c8] irq_exit+0x108/0x150
[c000001fffe97f10] [c000000000017bf4] __do_irq+0x2a4/0x4a0
[c000001fffe97f90] [c00000000002da50] call_do_irq+0x14/0x24
[c0000007fad93aa0] [c000000000017e8c] do_IRQ+0x9c/0x140
[c0000007fad93af0] [c000000000008b98] hardware_interrupt_common+0x138/0x140
--- interrupt: 501 at .L1.42+0x0/0x4
    LR = arch_local_irq_restore.part.4+0x84/0xb0
[c0000007fad93de0] [c0000007ffc1f7d8] 0xc0000007ffc1f7d8 (unreliable)
[c0000007fad93e00] [c000000000988d3c] cpuidle_enter_state+0x1bc/0x530
[c0000007fad93e60] [c0000000001457cc] call_cpuidle+0x4c/0x90
[c0000007fad93e80] [c000000000145b28] do_idle+0x208/0x2f0
[c0000007fad93ef0] [c000000000145f8c] cpu_startup_entry+0x3c/0x50
[c0000007fad93f20] [c000000000042bc0] start_secondary+0x3b0/0x4b0
[c0000007fad93f90] [c00000000000ac6c] start_secondary_prolog+0x10/0x14