linux-kernel - Re: [PATCH V2] hid: hid-core: Fix a sleep-in-atomic-context bug in __hid

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Date:   Sat, 29 Sep 2018 21:20:07 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
cc:     benjamin.tissoires@...hat.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] hid: hid-core: Fix a sleep-in-atomic-context bug in
 __hid_request()

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).

-- 
Jiri Kosina
SUSE Labs