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

[Jia-Ju Bai <baijiaju1990@gmail.com>]

On 2018/9/30 3:20, Jiri Kosina wrote:
> On Sat, 29 Sep 2018, Jia-Ju Bai wrote:
>
>>>> 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.
> Why? Forcing all the report buffer to be limited to be non-sleeping
> allocations just because of two drivers, looks like an overkill, and
> actually calls for more issues (as GFP_ATOMIC is of course in principle
> less likely to succeed).
>

Okay, I thought that using GFP_ATOMIC is the simplest way to fix these bugs.
But I check the Linux kernel code again, and find that hid_hw_request() 
are called at many places.
So changing this function may affect many drivers.
I agree to only change the two drivers, and explicitly anotate 
__hid_request() with might_sleep().


Best wishes,
Jia-Ju Bai