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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 >>>> Signed-off-by: Lianqin Hu >>>> --- >>>> >>>> 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