Subject: Re: [PATCH v4 2/7] Input: use input_device_enabled()

From: Dmitry Torokhov <[email-masked]>
Date: Tue, 8 Dec 2020 22:37:40 -0800

On Tue, Dec 08, 2020 at 11:05:42AM +0100, Marek Szyprowski wrote:
> Hi Andrzej,
> 
> On 07.12.2020 16:50, Andrzej Pietrasiewicz wrote:
> > Hi Marek,
> >
> > W dniu 07.12.2020 o 14:32, Marek Szyprowski pisze:
> >> Hi Andrzej,
> >>
> >> On 08.06.2020 13:22, Andrzej Pietrasiewicz wrote:
> >>> Use the newly added helper in relevant input drivers.
> >>>
> >>> Signed-off-by: Andrzej Pietrasiewicz <[email-masked]>
> >>
> >> This patch landed recently in linux-next as commit d69f0a43c677 ("Input:
> >> use input_device_enabled()"). Sadly it causes following warning during
> >> system suspend/resume cycle on ARM 32bit Samsung Exynos5250-based Snow
> >> Chromebook with kernel compiled from exynos_defconfig:
> >>
> >> ------------[ cut here ]------------
> >> WARNING: CPU: 0 PID: 1777 at drivers/input/input.c:2230
> >> input_device_enabled+0x68/0x6c
> >> Modules linked in: cmac bnep mwifiex_sdio mwifiex sha256_generic
> >> libsha256 sha256_arm cfg80211 btmrvl_sdio btmrvl bluetooth s5p_mfc
> >> exynos_gsc v4l2_mem2mem videob
> >> CPU: 0 PID: 1777 Comm: rtcwake Not tainted
> >> 5.10.0-rc6-next-20201207-00001-g49a0dc04c46d-dirty #9902
> >> Hardware name: Samsung Exynos (Flattened Device Tree)
> >> [<c0111718>] (unwind_backtrace) from [<c010d050>] (show_stack+0x10/0x14)
> >> [<c010d050>] (show_stack) from [<c0b32810>] (dump_stack+0xb4/0xd4)
> >> [<c0b32810>] (dump_stack) from [<c0126e24>] (__warn+0xd8/0x11c)
> >> [<c0126e24>] (__warn) from [<c0126f18>] (warn_slowpath_fmt+0xb0/0xb8)
> >> [<c0126f18>] (warn_slowpath_fmt) from [<c07fa2fc>]
> >> (input_device_enabled+0x68/0x6c)
> >> [<c07fa2fc>] (input_device_enabled) from [<c080a0f8>]
> >
> > Apparently you are hitting this line of code in drivers/input/input.c:
> >
> > lockdep_assert_held(&dev->mutex);
> >
> > Inspecting input device's "users" member should happen under dev's lock.
> >
> This check and warning has been introduced by this patch. I assume that 
> the suspend/resume paths are correct, but it looks that they were not 
> tested with this patch thus it has not been noticed that they are not 
> called under the input's lock. This needs a fix. Dmitry: how would you 
> like to handle this issue?

The check is proper and the warning is legit, cyapa should not be
checking this field without holding the lock. I think we can simply
remove this check from the power ops for gen3 and gen5, and this should
shut up the warning on suspend, but there other places in cyapa that do
check 'users', and they also need to be fixed.

Thanks.

-- 
Dmitry

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