Re: [PATCH v3] usb: gadget: u_serial: Disable ep before setting port to null to fix the crash caused by port being null

[Jon Hunter <jonathanh@nvidia.com>]

On 16/01/2025 15:01, Jon Hunter wrote:
> 
> On 16/01/2025 13:28, gregkh@linuxfoundation.org wrote:
>> On Thu, Jan 16, 2025 at 01:11:36PM +0000, Jon Hunter wrote:
>>> Hi Greg, Lianqin,
>>>
>>> On 17/12/2024 07:58, 胡连勤 wrote:
>>>> From: Lianqin Hu <hulianqin@vivo.com>
>>>>
>>>> Considering that in some extreme cases, when performing the
>>>> unbinding operation, gserial_disconnect has cleared gser->ioport,
>>>> which triggers gadget reconfiguration, and then calls gs_read_complete,
>>>> resulting in access to a null pointer. Therefore, ep is disabled before
>>>> gserial_disconnect sets port to null to prevent this from happening.
>>>>
>>>> Call trace:
>>>>    gs_read_complete+0x58/0x240
>>>>    usb_gadget_giveback_request+0x40/0x160
>>>>    dwc3_remove_requests+0x170/0x484
>>>>    dwc3_ep0_out_start+0xb0/0x1d4
>>>>    __dwc3_gadget_start+0x25c/0x720
>>>>    kretprobe_trampoline.cfi_jt+0x0/0x8
>>>>    kretprobe_trampoline.cfi_jt+0x0/0x8
>>>>    udc_bind_to_driver+0x1d8/0x300
>>>>    usb_gadget_probe_driver+0xa8/0x1dc
>>>>    gadget_dev_desc_UDC_store+0x13c/0x188
>>>>    configfs_write_iter+0x160/0x1f4
>>>>    vfs_write+0x2d0/0x40c
>>>>    ksys_write+0x7c/0xf0
>>>>    __arm64_sys_write+0x20/0x30
>>>>    invoke_syscall+0x60/0x150
>>>>    el0_svc_common+0x8c/0xf8
>>>>    do_el0_svc+0x28/0xa0
>>>>    el0_svc+0x24/0x84
>>>>
>>>> Fixes: c1dca562be8a ("usb gadget: split out serial core")
>>>> Cc: stable@vger.kernel.org
>>>> Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>> Signed-off-by: Lianqin Hu <hulianqin@vivo.com>
>>>> ---
>>>>
>>>> Changes in v3:
>>>>    - Add --- line above the version tag information
>>>>    - Remove extra blank lines in commit messages
>>>>    - Version tag information from v2 to changes in v2
>>>>    - Link to v2: https://lore.kernel.org/all/ 
>>>> TYUPR06MB6217DAA095A9863D4B58D57CD23B2@TYUPR06MB6217.apcprd06.prod.outlook.com/
>>>>
>>>> Changes in v2:
>>>>    - Remove some address information from patch descriptions
>>>>    - Link to v1: https://lore.kernel.org/all/ 
>>>> TYUPR06MB621763AB815989161F4033AFD2762@TYUPR06MB6217.apcprd06.prod.outlook.com/
>>>>    - Link to suggestions: https://lore.kernel.org/all/ 
>>>> TYUPR06MB6217DE28012FFEC5E808DD64D2962@TYUPR06MB6217.apcprd06.prod.outlook.com/
>>>>
>>>>    drivers/usb/gadget/function/u_serial.c | 8 ++++----
>>>>    1 file changed, 4 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/ 
>>>> gadget/function/u_serial.c
>>>> index 53d9fc41acc5..bc143a86c2dd 100644
>>>> --- a/drivers/usb/gadget/function/u_serial.c
>>>> +++ b/drivers/usb/gadget/function/u_serial.c
>>>> @@ -1420,6 +1420,10 @@ void gserial_disconnect(struct gserial *gser)
>>>>        /* REVISIT as above: how best to track this? */
>>>>        port->port_line_coding = gser->port_line_coding;
>>>> +    /* disable endpoints, aborting down any active I/O */
>>>> +    usb_ep_disable(gser->out);
>>>> +    usb_ep_disable(gser->in);
>>>> +
>>>>        port->port_usb = NULL;
>>>>        gser->ioport = NULL;
>>>>        if (port->port.count > 0) {
>>>> @@ -1431,10 +1435,6 @@ void gserial_disconnect(struct gserial *gser)
>>>>        spin_unlock(&port->port_lock);
>>>>        spin_unlock_irqrestore(&serial_port_lock, flags);
>>>> -    /* disable endpoints, aborting down any active I/O */
>>>> -    usb_ep_disable(gser->out);
>>>> -    usb_ep_disable(gser->in);
>>>> -
>>>>        /* finally, free any unused/unusable I/O buffers */
>>>>        spin_lock_irqsave(&port->port_lock, flags);
>>>>        if (port->port.count == 0)
>>>
>>>
>>> We have observed a reboot regression on Tegra234 (I have not tried other
>>> boards) and bisect is pointing to this commit. Reverting this on top of
>>> mainline is fixing the problem.
>>>
>>> With this change, when the board reboots we see ...
>>>
>>> [   59.918177] tegra-xudc 3550000.usb: ep 3 disabled
>>> [   59.923097] tegra-xudc 3550000.usb: ep 2 disabled
>>> [   59.927955] tegra-xudc 3550000.usb: ep 5 disabled
>>> [   80.911432] rcu: INFO: rcu_preempt self-detected stall on CPU
>>> [   80.917354] rcu:     6-....: (5248 ticks this GP) 
>>> idle=ec24/1/0x4000000000000000 softirq=1213/1213 fqs=2623
>>> [   80.927146] rcu:     (t=5253 jiffies g=3781 q=1490 ncpus=12)
>>> [   80.932704] Sending NMI from CPU 6 to CPUs 2:
>>> [   90.981555] CPU: 6 UID: 0 PID: 18 Comm: rcu_exp_gp_kthr Not 
>>> tainted 6.13.0-rc7-00043-g619f0b6fad52 #1
>>> [   90.981558] Hardware name: NVIDIA NVIDIA Jetson AGX Orin Developer 
>>> Kit/Jetson, BIOS 00.0.0-dev-main_92e5ae_88fd1_296de 12/16/2024
>>> [   90.981559] pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS 
>>> BTYPE=--)
>>> [   90.981562] pc : smp_call_function_single+0xdc/0x1a0
>>> [   90.981574] lr : __sync_rcu_exp_select_node_cpus+0x228/0x3c0
>>> [   90.981578] sp : ffff800082eb3cd0
>>> [   90.981579] x29: ffff800082eb3cd0 x28: 0000000000000010 x27: 
>>> ffff0000802933c0
>>> [   90.981582] x26: ffff0007a8a1d700 x25: ffff800082895500 x24: 
>>> ffff800080132018
>>> [   90.981584] x23: 0000000000000014 x22: ffff800081fb7700 x21: 
>>> ffff80008280d970
>>> [   90.981586] x20: 0000000000000feb x19: ffff800082eb3d00 x18: 
>>> 0000000000000000
>>> [   90.981588] x17: 0000000000000000 x16: 0000000000000000 x15: 
>>> 0000000000000000
>>> [   90.981590] x14: ffff000080293440 x13: 0000000000000001 x12: 
>>> 0000000000000000
>>> [   90.981591] x11: ffff800081fb2388 x10: ffff0000802933c0 x9 : 
>>> 0000000000000001
>>> [   90.981593] x8 : 0000000000000040 x7 : 0000000000017068 x6 : 
>>> ffff800080132018
>>> [   90.981595] x5 : 0000000000000000 x4 : ffff0007a8a4f9c8 x3 : 
>>> 0000000000000001
>>> [   90.981597] x2 : 0000000000000000 x1 : ffff0007a8a4f9c0 x0 : 
>>> 0000000000000004
>>> [   90.981599] Call trace:
>>> [   90.981601]  smp_call_function_single+0xdc/0x1a0 (P)
>>> [   90.981605]  __sync_rcu_exp_select_node_cpus+0x228/0x3c0
>>> [   90.981607]  sync_rcu_exp_select_cpus+0x13c/0x2a0
>>> [   90.981609]  wait_rcu_exp_gp+0x18/0x30
>>> [   90.981611]  kthread_worker_fn+0xd0/0x188
>>> [   90.981614]  kthread+0x118/0x11c
>>> [   90.981619]  ret_from_fork+0x10/0x20
>>> [  101.416347] sched: DL replenish lagged too much
>>>
>>
>> Odd, you have a usb-serial gadget device in this system that is
>> disconnecting somehow?  That oops doesn't point to anything in the usb
>> gadget codebase, "all" we have done is move the call to shutdown the
>> endpoints to earlier in the disconnect function.
> 
> Yes the board starts usb-serial and usb-ethernet gadget and on reboot 
> when tearing it down I am seeing the above. As soon as it disables the 
> tegra-xudc endpoints (as seen above) the board appears to stall.
> 
>> I'm glad to revert this, but it feels really odd that this is causing
>> you an rcu stall issue.
> 
> Thanks. I can't say I understand it either, but I am certain it is 
> caused by this change.
> 
> Happy to run any tests to narrow this down a bit.


I did a bit more looking at this and I see that we setup a USB gadget 
device via the configfs as described in this doc [0]. The RCU stall 
occurs when we attempt to disable the gadget on shutdown by ...

  $ echo "" > /path/to/UDC

Jon

[0] https://docs.kernel.org/usb/gadget_configfs.html

-- 
nvpublic