linux-kernel - Re: [PATCH v2 11/25] usb: gadget: f_tcm: Execute command on write completion

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Date:   Fri, 26 Aug 2022 18:37:36 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Bogdanov <d.bogdanov@...ro.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>
Subject: Re: [PATCH v2 11/25] usb: gadget: f_tcm: Execute command on write
 completion

On Fri, Aug 26, 2022, Sebastian Andrzej Siewior wrote:
> On 2022-07-18 18:27:12 [-0700], Thinh Nguyen wrote:
> > index 6fea80afe2d7..ec83f2f9a858 100644
> > --- a/drivers/usb/gadget/function/f_tcm.c
> > +++ b/drivers/usb/gadget/function/f_tcm.c
> > @@ -955,7 +949,7 @@ static void usbg_data_write_cmpl(struct usb_ep *ep, struct usb_request *req)
> >  				se_cmd->data_length);
> >  	}
> >  
> > -	complete(&cmd->write_complete);
> > +	target_execute_cmd(se_cmd);
> 
> usbg_data_write_cmpl() is invoked from interrupt service routing which
> may run with disabled interrupts. From looking at target_execute_cmd():

It will always be called with interrupts disabled as documented in
usb_request API.

> | void target_execute_cmd(struct se_cmd *cmd)
> | {
> …
> |         spin_lock_irq(&cmd->t_state_lock);
> …
> |         spin_unlock_irq(&cmd->t_state_lock);
> …
> | }
> 
> which means interrupts will remain open after leaving
> target_execute_cmd(). Now, why didn't the WARN_ONCE() in
> __handle_irq_event_percpu() trigger? Am I missing something?
> 
> >  	return;
> 

Since target_execute_cmd() is called in usbg_data_write_cmpl(),
interrupts are still disabled.

Thanks,
Thinh