Re: [PATCH V2] hid: hid-core: Fix a sleep-in-atomic-context bug in __hid_request()

[Jia-Ju Bai]

On 2018/9/24 17:26, Jiri Kosina wrote:
> On Thu, 13 Sep 2018, Jia-Ju Bai wrote:
>
> > hid_alloc_report_buf() has to be called with GFP_ATOMIC in
> > __hid_request(), because there are the following callchains
> > leading to __hid_request() being an atomic context:
> >
> > picolcd_send_and_wait (acquire a spinlock)
> >    hid_hw_request
> >      __hid_request
> >        hid_alloc_report_buf(GFP_KERNEL)
> >
> > picolcd_reset (acquire a spinlock)
> >    hid_hw_request
> >      __hid_request
> >        hid_alloc_report_buf(GFP_KERNEL)
> >
> > lg4ff_play (acquire a spinlock)
> >    hid_hw_request
> >      __hid_request
> >        hid_alloc_report_buf(GFP_KERNEL)
> >
> > lg4ff_set_autocenter_ffex (acquire a spinlock)
> >    hid_hw_request
> >      __hid_request
> >        hid_alloc_report_buf(GFP_KERNEL)
> Hm, so it's always drivers calling out into core in atomic context. So
> either we take this, and put our bets on being able to allocate the buffer
> without sleeping,

In my opinion, I prefer this way.


Best wishes,
Jia-Ju Bai

> or actually fix the few drivers (it's just lg4ff and
> picolcd at the end of the day) not to do that, and explicitly anotate
> __hid_request() with might_sleep().
>
> Hmm?
>
> Thanks,