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Date:   Wed, 5 Sep 2018 10:29:29 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     Jia-Ju Bai <baijiaju1990@gmail.com>
cc:     benjamin.tissoires@redhat.com, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hid: hid-core: Fix a sleep-in-atomic-context bug in
 __hid_request()
In-Reply-To: <20180901121659.1257-1-baijiaju1990@gmail.com>
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References: <20180901121659.1257-1-baijiaju1990@gmail.com>
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On Sat, 1 Sep 2018, Jia-Ju Bai wrote:

> The driver may sleep with holding a spinlock.
> 
> The function call paths (from bottom to top) in Linux-4.16 are:
> 
> [FUNC] hid_alloc_report_buf(GFP_KERNEL)
> drivers/hid/hid-core.c, 1435: 
> 	hid_alloc_report_buf in __hid_request
> ./include/linux/hid.h, 1023: 
> 	__hid_request in hid_hw_request
> drivers/hid/hid-picolcd_core.c, 111: 
> 	hid_hw_request in picolcd_send_and_wait
> drivers/hid/hid-picolcd_core.c, 100: 
> 	_raw_spin_lock_irqsave in picolcd_send_and_wait
> 
> [FUNC] hid_alloc_report_buf(GFP_KERNEL)
> drivers/hid/hid-core.c, 1435: 
> 	hid_alloc_report_buf in __hid_request
> ./include/linux/hid.h, 1023: 
> 	__hid_request in hid_hw_request
> drivers/hid/hid-picolcd_core.c, 245: 
> 	hid_hw_request in picolcd_reset
> drivers/hid/hid-picolcd_core.c, 235: 
> 	_raw_spin_lock_irqsave in picolcd_reset
> 
> [FUNC] hid_alloc_report_buf(GFP_KERNEL)
> drivers/hid/hid-core.c, 1435: 
> 	hid_alloc_report_buf in __hid_request
> ./include/linux/hid.h, 1023: 
> 	__hid_request in hid_hw_request
> drivers/hid/hid-picolcd_fb.c, 215: 
> 	hid_hw_request in picolcd_fb_reset
> drivers/hid/hid-picolcd_fb.c, 206: 
> 	_raw_spin_lock_irqsave in picolcd_fb_reset
> 
> [FUNC] hid_alloc_report_buf(GFP_KERNEL)
> drivers/hid/hid-core.c, 1435: 
> 	hid_alloc_report_buf in __hid_request
> ./include/linux/hid.h, 1023: 
> 	__hid_request in hid_hw_request
> drivers/hid/hid-lg4ff.c, 465: 
> 	hid_hw_request in lg4ff_play
> drivers/hid/hid-lg4ff.c, 441: 
> 	_raw_spin_lock_irqsave in lg4ff_play
> 
> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.
> 
> This bug is found by my static analysis tool DSAC.

Could you please rewrite the changelog so that it's human readable? The 
above is a bit hard to understand, I think something along the lines of 
"__hid_request() has to be allocating with GFP_ATOMIC because there are 
the following callchains leading to __hid_request() being an atomic 
context: ... a->b->c.._hid_request()" etc.

Thanks,

-- 
Jiri Kosina
SUSE Labs