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

[Andrew Davis]

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