On 2018/9/24 17:26, Jiri Kosina wrote:

On Thu, 13 Sep 2018, Jia-Ju Bai wrote:

quoted

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,