Re: [PATCH v2] mailbox: PCC: Fix lockdep warning when request PCC channel

[Prakash, Prashanth]

Hi Hoan,

On 10/18/2016 1:00 AM, Hoan Tran wrote:
> This patch fixes the lockdep warning below
>
> [    7.229767] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> [    7.229776] ------------[ cut here ]------------
> [    7.229787] WARNING: CPU: 1 PID: 1 at linux-next/kernel/locking/lockdep.c:2876 loc
> kdep_trace_alloc+0xe0/0xf0
> [    7.229790] Modules linked in:
> [    7.229793]
> [    7.229798] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.8.0-11756-g86c5152 #46
> ...
> [    7.229900] Call trace:
> [    7.229903] Exception stack(0xffff8007da837890 to 0xffff8007da8379c0)
> [    7.229906] 7880:                                   ffff8007da834000 0001000000000000
> [    7.229909] 78a0: ffff8007da837a70 ffff0000081111a0 00000000600000c5 000000000000003d
> [    7.229912] 78c0: 9374bc6a7f3c7832 0000000000381878 ffff000009db7ab8 000000000000002f
> [    7.229915] 78e0: ffff00000811aabc ffff000008be2548 ffff8007da837990 ffff00000811adf8
> [    7.229918] 7900: ffff8007da834000 00000000024080c0 00000000000000c0 ffff000009021000
> [    7.229921] 7920: 0000000000000000 0000000000000000 ffff000008c8f7c8 ffff8007da579810
> [    7.229923] 7940: 000000000000002f ffff8007da858000 0000000000000000 0000000000000001
> [    7.229926] 7960: 0000000000000001 0000000000000000 ffff00000811a468 0000000000000002
> [    7.229929] 7980: 656c62617369645f 0000000000038187 00000000000000ee ffff8007da837850
> [    7.229932] 79a0: ffff000009db50c0 ffff000009db569d 0000000000000006 ffff000089db568f
> [    7.229936] [<ffff0000081111a0>] lockdep_trace_alloc+0xe0/0xf0
> [    7.229940] [<ffff0000081f4950>] __kmalloc_track_caller+0x50/0x250
> [    7.229945] [<ffff00000857c088>] devres_alloc_node+0x28/0x60
> [    7.229949] [<ffff0000081220e0>] devm_request_threaded_irq+0x50/0xe0
> [    7.229955] [<ffff0000087e6220>] pcc_mbox_request_channel+0x110/0x170
> [    7.229960] [<ffff0000084b2660>] acpi_cppc_processor_probe+0x264/0x414
> [    7.229963] [<ffff0000084ae9f4>] __acpi_processor_start+0x28/0xa0
> [    7.229966] [<ffff0000084aeab0>] acpi_processor_start+0x44/0x54
> [    7.229970] [<ffff00000857897c>] driver_probe_device+0x1fc/0x2b0
> [    7.229974] [<ffff000008578ae4>] __driver_attach+0xb4/0xc0
> [    7.229977] [<ffff00000857683c>] bus_for_each_dev+0x5c/0xa0
> [    7.229980] [<ffff000008578110>] driver_attach+0x20/0x30
> [    7.229983] [<ffff000008577c20>] bus_add_driver+0x110/0x230
> [    7.229987] [<ffff000008579320>] driver_register+0x60/0x100
> [    7.229991] [<ffff000008d478b8>] acpi_processor_driver_init+0x2c/0xb0
> [    7.229996] [<ffff000008083168>] do_one_initcall+0x38/0x130
> [    7.230000] [<ffff000008d20d6c>] kernel_init_freeable+0x210/0x2b4
> [    7.230004] [<ffff000008945d90>] kernel_init+0x10/0x110
> [    7.230007] [<ffff000008082e80>] ret_from_fork+0x10/0x50
>
> It's because the spinlock inside pcc_mbox_request_channel() is
> kept too long. This patch releases spinlock before request_irq()
> and free_irq() to fix this issue  as spinlock is only needed to
> protect the channel data.
>
> Signed-off-by: Hoan Tran <hotran@xxxxxxx>
> ---
> v2
>  * Release spinlock before request_irq() and free_irq() instead of
> using mutex
>
>  drivers/mailbox/pcc.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> index 08c87fa..b5275a8 100644
> --- a/drivers/mailbox/pcc.c
> +++ b/drivers/mailbox/pcc.c
> @@ -267,6 +267,8 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
>  	if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
>  		chan->txdone_method |= TXDONE_BY_ACK;
>  
> +	spin_unlock_irqrestore(&chan->lock, flags);
> +
>  	if (pcc_doorbell_irq[subspace_id] > 0) {
>  		int rc;
>  
> @@ -279,8 +281,6 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
>  		}
>  	}
>  
> -	spin_unlock_irqrestore(&chan->lock, flags);
> -
>  	return chan;
>  }
>  EXPORT_SYMBOL_GPL(pcc_mbox_request_channel);
> @@ -310,10 +310,10 @@ void pcc_mbox_free_channel(struct mbox_chan *chan)
>  	if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
>  		chan->txdone_method = TXDONE_BY_POLL;
>  
> +	spin_unlock_irqrestore(&chan->lock, flags);
> +
>  	if (pcc_doorbell_irq[id] > 0)
>  		devm_free_irq(chan->mbox->dev, pcc_doorbell_irq[id], chan);
Shouldn't we free the irq first and then reset the channel state?
To avoid the scenario where an interrupt might get triggered after
we reset the channel state but before we release the interrupt

--
Thanks,
Prashanth