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([2001:a61:13ed:c201:b884:edfc:abaf:1cf4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-378e780e14fsm8894819f8f.117.2024.09.17.01.33.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Sep 2024 01:33:22 -0700 (PDT) Message-ID: Date: Tue, 17 Sep 2024 10:33:21 +0200 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] usb: use mutex_lock in iowarrior_read() To: Jeongjun Park , Oliver Neukum Cc: Greg KH , colin.i.king@gmail.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240916040629.28750-1-aha310510@gmail.com> <2024091648-excusable-unfilled-83de@gregkh> <15bc0f3a-5433-43e0-b0b0-8b9c26dec165@suse.com> Content-Language: en-US From: Oliver Neukum In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.09.24 08:23, Jeongjun Park wrote: > Oliver Neukum wrote: > Okay. But O_NONBLOCK flag check already exists, and I don't know > if we need to branch separately to mutex_trylock just because O_NONBLOCK > flag exists. I think mutex_lock_interruptible is enough. It will still block. > And the point of locking is too late. I think it would be more appropriate to > read file->private_data and then lock it right away. You are right. dev->present should be checked under the lock only. > I think this patch is a more appropriate patch: > > --- > drivers/usb/misc/iowarrior.c | 41 +++++++++++++++++++++++++++--------- > 1 file changed, 31 insertions(+), 10 deletions(-) > > diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c > index 6d28467ce352..6fb4ecebbc15 100644 > --- a/drivers/usb/misc/iowarrior.c > +++ b/drivers/usb/misc/iowarrior.c > @@ -277,28 +277,40 @@ static ssize_t iowarrior_read(struct file *file, > char __user *buffer, > struct iowarrior *dev; > int read_idx; > int offset; > + int retval = 0; > > dev = file->private_data; > > + if (mutex_lock_interruptible(&dev->mutex)) { This blocks. To quote the man page: O_NONBLOCK or O_NDELAY When possible, the file is opened in nonblocking mode. Neither the open() nor any subsequent I/O operations on the file descriptor which is returned will cause the calling process to wait. [..] > +unlock_exit: > + mutex_unlock(&dev->mutex); > +exit: > + return retval; The rest looks good to me. Regards Oliver