Re: [PATCH] mailbox: mtk-cmdq: Fix sleeping function called from invalid context

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 30/04/24 10:39, Jason-JH.Lin ha scritto:
> When we run kernel with lockdebug option, we will get the BUG below:
> [  106.692124] BUG: sleeping function called from invalid context at drivers/base/power/runtime.c:1164
> [  106.692190] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 3616, name: kworker/u17:3
> [  106.692226] preempt_count: 1, expected: 0
> [  106.692254] RCU nest depth: 0, expected: 0
> [  106.692282] INFO: lockdep is turned off.
> [  106.692306] irq event stamp: 0
> [  106.692331] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [  106.692376] hardirqs last disabled at (0): [<ffffffee15d37fa0>] copy_process+0xc90/0x2ac0
> [  106.692429] softirqs last  enabled at (0): [<ffffffee15d37fc4>] copy_process+0xcb4/0x2ac0
> [  106.692473] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [  106.692513] CPU: 1 PID: 3616 Comm: kworker/u17:3 Not tainted 6.1.87-lockdep-14133-g26e933aca785 #1 6839942e1cf34914b0a366137843dd2366f52aa9
> [  106.692556] Hardware name: Google Ciri sku0/unprovisioned board (DT)
> [  106.692586] Workqueue: imgsys_runner imgsys_runner_func
> [  106.692638] Call trace:
> [  106.692662]  dump_backtrace+0x100/0x120
> [  106.692702]  show_stack+0x20/0x2c
> [  106.692737]  dump_stack_lvl+0x84/0xb4
> [  106.692775]  dump_stack+0x18/0x48
> [  106.692809]  __might_resched+0x354/0x4c0
> [  106.692847]  __might_sleep+0x98/0xe4
> [  106.692883]  __pm_runtime_resume+0x70/0x124
> [  106.692921]  cmdq_mbox_send_data+0xe4/0xb1c
> [  106.692964]  msg_submit+0x194/0x2dc
> [  106.693003]  mbox_send_message+0x190/0x330
> [  106.693043]  imgsys_cmdq_sendtask+0x1618/0x2224
> [  106.693082]  imgsys_runner_func+0xac/0x11c
> [  106.693118]  process_one_work+0x638/0xf84
> [  106.693158]  worker_thread+0x808/0xcd0
> [  106.693196]  kthread+0x24c/0x324
> [  106.693231]  ret_from_fork+0x10/0x20
> 
> We found that there is a spin_lock_irqsave protection in msg_submit()
> of mailbox.c.
> So when cmdq driver calls pm_runtime_get_sync() in cmdq_mbox_send_data(),
> it will get this BUG report.
> 
> Add pm_runtime_irq_safe() to let pm_runtime callbacks is safe in atomic
> context with interrupts disabled.
> 

I see. The problem with this is that pm_runtime_irq_safe() will raise the refcount
of the parent device "forever", which isn't the best and partially defeats what we
are trying to do here (keeping stuff off unless really needed).

At this point I wonder if it'd be just better to really fix this instead of working
around the problem.

I'd say that one of the options would be to perform a change to msg_submit() so
that it will take into account that a .send_data() callback might be using RPM
functions.

Ideas? :-)

Cheers,
Angelo

> Fixes: 8afe816b0c99 ("mailbox: mtk-cmdq-mailbox: Implement Runtime PM with autosuspend")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
> ---
>   drivers/mailbox/mtk-cmdq-mailbox.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/mailbox/mtk-cmdq-mailbox.c b/drivers/mailbox/mtk-cmdq-mailbox.c
> index ead2200f39ba..3b4f19633c83 100644
> --- a/drivers/mailbox/mtk-cmdq-mailbox.c
> +++ b/drivers/mailbox/mtk-cmdq-mailbox.c
> @@ -694,6 +694,7 @@ static int cmdq_probe(struct platform_device *pdev)
>   
>   	pm_runtime_set_autosuspend_delay(dev, CMDQ_MBOX_AUTOSUSPEND_DELAY_MS);
>   	pm_runtime_use_autosuspend(dev);
> +	pm_runtime_irq_safe(dev);
>   
>   	return 0;
>   }