linux-kernel - Re: [PATCH v2 00/13] OMAP mailbox FIFO removal

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Date: Thu, 13 Jun 2024 07:22:57 -0500
From: Andrew Davis <afd@...com>
To: Dominic Rath <dominic.rath@...-augsburg.net>,
        Jassi Brar
	<jassisinghbrar@...il.com>, Hari Nagalla <hnagalla@...com>,
        Nick Saulnier
	<nsaulnier@...com>,
        Bjorn Andersson <andersson@...nel.org>,
        Mathieu Poirier
	<mathieu.poirier@...aro.org>
CC: <linux-remoteproc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 00/13] OMAP mailbox FIFO removal

On 6/13/24 2:58 AM, Dominic Rath wrote:
> Hello Andrew,
> 
> On 10.04.2024 15:59, Andrew Davis wrote:
>> Changes for v2:
>>   - Use threaded irq as suggested by Hari and to
>>       fix possible "scheduling while atomic" issue
> 
> sorry for beeing late, I noticed this already got merged.
> 
> I was wondering what the reason was for ending up with the
> threaded irq.
> 
> In your v1 thread your final conclusion appeared to be
> 
>> So for now I just kept this using the regular IRQ context as before.
> 
> We looked into this some time ago, and noticed that the IRQ approach caused problems in the virtio/rpmsg code. I'd like to understand if your change was for the same reason, or something else we missed before.
> 

It is most likely the same reason. Seems despite its name, rproc_vq_interrupt() cannot
be called from an IRQ/atomic context. As the following backtrace shows, that function
calls down into functions which are not IRQ safe. So we needed to keep it threaded:

[    5.389374] BUG: scheduling while atomic: (udev-worker)/232/0x00010002
[    5.395917] Modules linked in: videobuf2_dma_contig videobuf2_memops videobuf2_v4l2 phy_j721e_wiz display_connector omap_mailbox(+) videodev tps6594_i2c(+) videobuf2_common phy_can_transceiver at24 cd6
[    5.433562] CPU: 0 PID: 232 Comm: (udev-worker) Not tainted 6.10.0-rc1-next-20240528-dirty #10
[    5.442158] Hardware name: Texas Instruments AM69 SK (DT)
[    5.447540] Call trace:
[    5.449976]  dump_backtrace+0x94/0xec
[    5.453640]  show_stack+0x18/0x24
[    5.456944]  dump_stack_lvl+0x78/0x90
[    5.460598]  dump_stack+0x18/0x24
[    5.463900]  __schedule_bug+0x50/0x68
[    5.467552]  __schedule+0x80c/0xb0c
[    5.471029]  schedule+0x34/0x104
[    5.474243]  schedule_preempt_disabled+0x24/0x40
[    5.478845]  rwsem_down_write_slowpath+0x31c/0x56c
[    5.483622]  down_write+0x90/0x94
[    5.486924]  kernfs_add_one+0x3c/0x148
[    5.490661]  kernfs_create_dir_ns+0x50/0x94
[    5.494830]  sysfs_create_dir_ns+0x70/0x10c
[    5.498999]  kobject_add_internal+0x98/0x26c
[    5.503254]  kobject_add+0x9c/0x10c
[    5.506729]  device_add+0xc0/0x790
[    5.510120]  rpmsg_register_device_override+0x10c/0x1c0
[    5.515333]  rpmsg_register_device+0x14/0x20
[    5.519590]  virtio_rpmsg_create_channel+0xb0/0x104
[    5.524452]  rpmsg_create_channel+0x28/0x60
[    5.528622]  rpmsg_ns_cb+0x100/0x1dc
[    5.532185]  rpmsg_recv_done+0x114/0x2e4
[    5.536094]  vring_interrupt+0x68/0xa4
[    5.539833]  rproc_vq_interrupt+0x2c/0x48
[    5.543830]  k3_r5_rproc_mbox_callback+0x84/0x90 [ti_k3_r5_remoteproc]
[    5.550348]  mbox_chan_received_data+0x1c/0x2c
[    5.554779]  mbox_interrupt+0xa0/0x17c [omap_mailbox]
[    5.559820]  __handle_irq_event_percpu+0x48/0x13c
[    5.564511]  handle_irq_event+0x4c/0xac

Andrew

> Regards,
> 
> Dominic