On Wed, 25 May 2022 at 03:12, AngeloGioacchino Del Regno
<angelogioacchino.delregno@xxxxxxxxxxxxx> wrote:
>
> During execution of the worker that's used to register rpmsg devices
> we are safely locking the channels mutex but, when creating a new
> endpoint for such devices, we are registering a IPI on the SCP, which
> then makes the SCP to trigger an interrupt, lock its own mutex and in
> turn register more subdevices.
> This creates a circular locking dependency situation, as the mtk_rpmsg
> channels_lock will then depend on the SCP IPI lock.
>
> [ 18.014514] Possible unsafe locking scenario:
> [ 18.014515] CPU0 CPU1
> [ 18.014517] ---- ----
> [ 18.045467] lock(&mtk_subdev->channels_lock);
> [ 18.045474] lock(&scp->ipi_desc[i].lock);
> [ 18.228399] lock(&mtk_subdev->channels_lock);
> [ 18.228405] lock(&scp->ipi_desc[i].lock);
> [ 18.264405]
>
> To solve this, simply unlock the channels_lock mutex before calling
> mtk_rpmsg_register_device() and relock it right after, as safety is
> still ensured by the locking mechanism that happens right after
> through SCP.
>
> Fixes: 7017996951fd ("rpmsg: add rpmsg support for mt8183 SCP.")
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
I have applied this patch.
Thanks,
Mathieu
> ---
>
> v2: Adding debug log to changelog portion, fixed commit description
>
> [ 15.447736] ======================================================
> [ 15.460158] WARNING: possible circular locking dependency detected
> [ 15.460161] 5.17.0-next-20220324+ #399 Not tainted
> [ 15.460165] ------------------------------------------------------
> [ 15.460166] kworker/0:3/155 is trying to acquire lock:
> [ 15.460170] ffff5b4d0eaf1308 (&scp->ipi_desc[i].lock){+.+.}-{4:4}, at: scp_ipi_lock+0x34/0x50 [mtk_scp_ipi]
> [ 15.504958]
> [] but task is already holding lock:
> [ 15.504960] ffff5b4d0e8f1918 (&mtk_subdev->channels_lock){+.+.}-{4:4}, at: mtk_register_device_work_function+0x50/0x1cc [mtk_rpmsg]
> [ 15.504978]
> [] which lock already depends on the new lock.
>
> [ 15.504980]
> [] the existing dependency chain (in reverse order) is:
> [ 15.504982]
> [] -> #1 (&mtk_subdev->channels_lock){+.+.}-{4:4}:
> [ 15.504990] lock_acquire+0x68/0x84
> [ 15.504999] __mutex_lock+0xa4/0x3e0
> [ 15.505007] mutex_lock_nested+0x40/0x70
> [ 15.505012] mtk_rpmsg_ns_cb+0xe4/0x134 [mtk_rpmsg]
> [ 15.641684] mtk_rpmsg_ipi_handler+0x38/0x64 [mtk_rpmsg]
> [ 15.641693] scp_ipi_handler+0xbc/0x180 [mtk_scp]
> [ 15.663905] mt8192_scp_irq_handler+0x44/0xa4 [mtk_scp]
> [ 15.663915] scp_irq_handler+0x6c/0xa0 [mtk_scp]
> [ 15.685779] irq_thread_fn+0x34/0xa0
> [ 15.685785] irq_thread+0x18c/0x240
> [ 15.685789] kthread+0x104/0x110
> [ 15.709579] ret_from_fork+0x10/0x20
> [ 15.709586]
> [] -> #0 (&scp->ipi_desc[i].lock){+.+.}-{4:4}:
> [ 15.731271] __lock_acquire+0x11e4/0x1910
> [ 15.740367] lock_acquire.part.0+0xd8/0x220
> [ 15.749813] lock_acquire+0x68/0x84
> [ 15.757861] __mutex_lock+0xa4/0x3e0
> [ 15.766084] mutex_lock_nested+0x40/0x70
> [ 15.775006] scp_ipi_lock+0x34/0x50 [mtk_scp_ipi]
> [ 15.785503] scp_ipi_register+0x40/0xa4 [mtk_scp_ipi]
> [ 15.796697] scp_register_ipi+0x1c/0x30 [mtk_scp]
> [ 15.807194] mtk_rpmsg_create_ept+0xa0/0x108 [mtk_rpmsg]
> [ 15.818912] rpmsg_create_ept+0x44/0x60
> [ 15.827660] cros_ec_rpmsg_probe+0x15c/0x1f0
> [ 15.837282] rpmsg_dev_probe+0x128/0x1d0
> [ 15.846203] really_probe.part.0+0xa4/0x2a0
> [ 15.855649] __driver_probe_device+0xa0/0x150
> [ 15.865443] driver_probe_device+0x48/0x150
> [ 15.877157] __device_attach_driver+0xc0/0x12c
> [ 15.889359] bus_for_each_drv+0x80/0xe0
> [ 15.900330] __device_attach+0xe4/0x190
> [ 15.911303] device_initial_probe+0x1c/0x2c
> [ 15.922969] bus_probe_device+0xa8/0xb0
> [ 15.933927] device_add+0x3a8/0x8a0
> [ 15.944193] device_register+0x28/0x40
> [ 15.954970] rpmsg_register_device+0x5c/0xa0
> [ 15.966782] mtk_register_device_work_function+0x148/0x1cc [mtk_rpmsg]
> [ 15.983146] process_one_work+0x294/0x664
> [ 15.994458] worker_thread+0x7c/0x45c
> [ 16.005069] kthread+0x104/0x110
> [ 16.014789] ret_from_fork+0x10/0x20
> [ 16.025201]
> [] other info that might help us debug this:
>
> [ 16.047769] Possible unsafe locking scenario:
>
> [ 16.063942] CPU0 CPU1
> [ 16.075166] ---- ----
> [ 16.086376] lock(&mtk_subdev->channels_lock);
> [ 16.097592] lock(&scp->ipi_desc[i].lock);
> [ 16.113188] lock(&mtk_subdev->channels_lock);
> [ 16.129482] lock(&scp->ipi_desc[i].lock);
> [ 16.140020]
> [] *** DEADLOCK ***
>
> [ 16.158282] 4 locks held by kworker/0:3/155:
> [ 16.168978] #0: ffff5b4d00008748 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1fc/0x664
> [ 16.190017] #1: ffff80000953bdc8 ((work_completion)(&mtk_subdev->register_work)){+.+.}-{0:0}, at: process_one_work+0x1fc/0x664
> [ 16.215269] #2: ffff5b4d0e8f1918 (&mtk_subdev->channels_lock){+.+.}-{4:4}, at: mtk_register_device_work_function+0x50/0x1cc [mtk_rpmsg]
> [ 16.242131] #3: ffff5b4d05964190 (&dev->mutex){....}-{4:4}, at: __device_attach+0x44/0x190
>
> drivers/rpmsg/mtk_rpmsg.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/rpmsg/mtk_rpmsg.c b/drivers/rpmsg/mtk_rpmsg.c
> index 5b4404b8be4c..d1213c33da20 100644
> --- a/drivers/rpmsg/mtk_rpmsg.c
> +++ b/drivers/rpmsg/mtk_rpmsg.c
> @@ -234,7 +234,9 @@ static void mtk_register_device_work_function(struct work_struct *register_work)
> if (info->registered)
> continue;
>
> + mutex_unlock(&subdev->channels_lock);
> ret = mtk_rpmsg_register_device(subdev, &info->info);
> + mutex_lock(&subdev->channels_lock);
> if (ret) {
> dev_err(&pdev->dev, "Can't create rpmsg_device\n");
> continue;
> --
> 2.35.1
>
