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([2402:f000:1:1501:200:5efe:a66f:4725]) by smtp.gmail.com with ESMTPSA id n13-v6sm9017545pgr.73.2018.09.29.02.00.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 29 Sep 2018 02:00:55 -0700 (PDT) Subject: Re: [PATCH V2] hid: hid-core: Fix a sleep-in-atomic-context bug in __hid_request() To: Jiri Kosina Cc: benjamin.tissoires@redhat.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180913033432.16336-1-baijiaju1990@gmail.com> From: Jia-Ju Bai Message-ID: <4c0096c6-3745-963c-5086-5f579792599b@gmail.com> Date: Sat, 29 Sep 2018 17:00:50 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/9/24 17:26, Jiri Kosina wrote: > On Thu, 13 Sep 2018, Jia-Ju Bai wrote: > >> 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, >