On Tue, 12 Jun 2018, Sebastian Andrzej Siewior wrote:

> In the code path
>   __usb_hcd_giveback_urb()
>   -> wdm_in_callback()
>    -> service_outstanding_interrupt()
> 
> The function service_outstanding_interrupt() will unconditionally enable
> interrupts during unlock and invoke usb_submit_urb() with GFP_KERNEL.
> If the HCD completes in BH (like ehci does) then the context remains
> atomic due local_bh_disable() and enabling interrupts does not change
> this.
> 
> Add an argument to service_outstanding_interrupt() which decides
> whether or not it is save to enable interrupts during unlocking and use
> GFP_KERNEL or not.
Wouldn't it be easier just to use spin_lock_irqsave() and GFP_ATOMIC
all the time?  That's what people normally do with code that can be 
called in both process and interrupt contexts.

Alan Stern

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