From: "Bruno Prémont" <bonbons@sysophe.eu>
To: Jia-Ju Bai <baijiaju1990@gmail.com>
Cc: "Bruno Prémont" <bonbons@linux-vserver.org>,
jikos@kernel.org, benjamin.tissoires@redhat.com,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hid: hid-picolcd: fix possible sleep-in-atomic-context bug
Date: Sun, 22 Dec 2019 19:37:39 +0100 [thread overview]
Message-ID: <20191222193739.76123ce7@hemera.lan.sysophe.eu> (raw)
In-Reply-To: <e36ad913-c498-4d5a-0a5a-bec016d49a16@gmail.com>
Hi Jia-Ju,
I've had a deeper look at the code (possibly also applies to hid-lg4ff).
The hdev->ll_driver->request (at least on USB bus which is the only one
that matters for hid-picolcd) points to:
usbhid_request() from drivers/hid/usbhid/hid-core.c
This one directly calls usbhid_submit_report() which then directly calls
__usbhid_submit_report() under spinlock.
Thus for USB bus there is no possible sleep left.
Just moving the hid_hw_request() calls out of the spinlock is
incorrect though as it would introduce the possibility of unexpected
concurrent initialization/submissions of reports from the distinct
sub-drivers. The report pointer used is not call-private but comes from
feature description and is filled with data on each call within the
spinlock.
The question could be whether the generic fallback in hid_hw_request()
should be adjusted to be non-sleeping.
It has been introduced rather more recently than both drivers you
detected.
Best regards,
Bruno Prémont
On Wed, 18 Dec 2019 20:11:47 Jia-Ju Bai wrote:
> Thanks for the reply.
>
> On 2019/12/18 16:41, Bruno Prémont wrote:
> > Hi Jia-Ju,
> >
> > Your checker has been looking at fallback implementation for
> > the might-sleep hid_alloc_report_buf(GFP_KERNEL).
> >
> > Did you have a look at the low-lever bus-driver implementations:
> > hdev->ll_driver->request
> > ^^^^^^^
> >
> > Are those all sleeping as well or maybe they don't sleep?\
>
> In fact, I find that a function possibly-related to this function
> pointer can sleep:
>
> drivers/hid/intel-ish-hid/ishtp-hid.c, 97:
> kzalloc(GFP_KERNEL) in ishtp_hid_request
>
> But I am not quite sure whether this function is really referenced by
> the function pointer, so I did not report it.
>
>
> Best wishes,
> Jia-Ju Bai
prev parent reply other threads:[~2019-12-22 18:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-18 8:02 [PATCH] hid: hid-picolcd: fix possible sleep-in-atomic-context bug Jia-Ju Bai
2019-12-18 8:41 ` Bruno Prémont
2019-12-18 12:11 ` Jia-Ju Bai
2019-12-22 18:37 ` Bruno Prémont [this message]
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