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[68.147.0.187]) by smtp.gmail.com with ESMTPSA id f15sm20685040pgg.23.2021.06.22.12.56.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Jun 2021 12:56:24 -0700 (PDT) Date: Tue, 22 Jun 2021 13:56:22 -0600 From: Mathieu Poirier To: Arnaud POULIQUEN Cc: Bjorn Andersson , Ohad Ben-Cohen , linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com Subject: Re: [PATCH v2 1/1] rpmsg: ctrl: Introduce new RPMSG_CREATE/RELEASE_DEV_IOCTL controls Message-ID: <20210622195622.GA1006507@p14s> References: <20210621125800.27696-1-arnaud.pouliquen@foss.st.com> <20210621125800.27696-2-arnaud.pouliquen@foss.st.com> <20210621231633.GC980846@p14s> <343c372e-0c0a-ad4e-356b-47eb975ce0e0@foss.st.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <343c372e-0c0a-ad4e-356b-47eb975ce0e0@foss.st.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 22, 2021 at 09:43:49AM +0200, Arnaud POULIQUEN wrote: > Hi Mathieu > > On 6/22/21 1:16 AM, Mathieu Poirier wrote: > > On Mon, Jun 21, 2021 at 02:58:00PM +0200, Arnaud Pouliquen wrote: > >> Allow the user space application to create and release an rpmsg device > >> by adding RPMSG_CREATE_DEV_IOCTL and RPMSG_RELEASE_DEV_IOCTL ioctrls to > >> the /dev/rpmsg_ctrl interface > >> > >> The RPMSG_CREATE_DEV_IOCTL Ioctl can be used to instantiate a local rpmsg > >> device. > >> Depending on the back-end implementation, the associated rpmsg driver is > >> probed and a NS announcement can be sent to the remote processor. > >> > >> The RPMSG_RELEASE_DEV_IOCTL allows the user application to release a > >> rpmsg device created either by the remote processor or with the > >> RPMSG_CREATE_DEV_IOCTL call. > >> Depending on the back-end implementation, the associated rpmsg driver is > >> removed and a NS destroy rpmsg can be sent to the remote processor. > >> > >> Suggested-by: Mathieu Poirier > >> Signed-off-by: Arnaud Pouliquen > >> --- > >> drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++++++---- > >> include/uapi/linux/rpmsg.h | 10 ++++++++++ > >> 2 files changed, 43 insertions(+), 4 deletions(-) > >> > >> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c > >> index eeb1708548c1..cb19e32d05e1 100644 > >> --- a/drivers/rpmsg/rpmsg_ctrl.c > >> +++ b/drivers/rpmsg/rpmsg_ctrl.c > >> @@ -23,6 +23,7 @@ > >> #include > >> > >> #include "rpmsg_char.h" > >> +#include "rpmsg_internal.h" > >> > >> static dev_t rpmsg_major; > >> > >> @@ -37,11 +38,13 @@ static DEFINE_IDA(rpmsg_minor_ida); > >> * @rpdev: underlaying rpmsg device > >> * @cdev: cdev for the ctrl device > >> * @dev: device for the ctrl device > >> + * @ctrl_lock: serialize the ioctrls. > >> */ > >> struct rpmsg_ctrldev { > >> struct rpmsg_device *rpdev; > >> struct cdev cdev; > >> struct device dev; > >> + struct mutex ctrl_lock; > >> }; > >> > >> static int rpmsg_ctrldev_open(struct inode *inode, struct file *filp) > >> @@ -70,9 +73,8 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd, > >> void __user *argp = (void __user *)arg; > >> struct rpmsg_endpoint_info eptinfo; > >> struct rpmsg_channel_info chinfo; > >> - > >> - if (cmd != RPMSG_CREATE_EPT_IOCTL) > >> - return -EINVAL; > >> + struct rpmsg_device *rpdev; > >> + int ret = 0; > >> > >> if (copy_from_user(&eptinfo, argp, sizeof(eptinfo))) > >> return -EFAULT; > >> @@ -82,7 +84,33 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd, > >> chinfo.src = eptinfo.src; > >> chinfo.dst = eptinfo.dst; > >> > >> - return rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo); > >> + mutex_lock(&ctrldev->ctrl_lock); > > > > Have you been able to verify the VFS layer doesn't take care of serializing > > ioctl() and file accesses in general? I did a quick search in the drivers/ > > directory and the vast majority of implementations don't use a lock. > > Please find my answer here https://lkml.org/lkml/2021/6/21/235 Ah ok, I hadn't noticed that one. > I tested by suppressing the lock and adding msleep to check a potential atomic. > in the rpmsg_ctrldev_ioctl function. Nothing seems prevent the re-entrance. Thanks for testing this out. I did some research on my side and turns out unlocked_ioctl() was introduced to get rid of the Big Kernel Lock rather than indicate that serialisation is not supported by this interface. Someone also asked the exact same question here [1]. So yes, locking is required. Reviewed-by: Mathieu Poirier [1]. https://stackoverflow.com/questions/18874962/linux-device-driver-file-operations-it-is-possible-to-have-race-conditions > > Regards, > Arnaud > > > > > Thanks, > > Mathieu > > > >> + switch (cmd) { > >> + case RPMSG_CREATE_EPT_IOCTL: > >> + ret = rpmsg_chrdev_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo); > >> + break; > >> + > >> + case RPMSG_CREATE_DEV_IOCTL: > >> + rpdev = rpmsg_create_channel(ctrldev->rpdev, &chinfo); > >> + if (!rpdev) { > >> + dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name); > >> + ret = -ENXIO; > >> + } > >> + break; > >> + > >> + case RPMSG_RELEASE_DEV_IOCTL: > >> + ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo); > >> + if (ret) > >> + dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n", > >> + chinfo.name, ret); > >> + break; > >> + > >> + default: > >> + ret = -EINVAL; > >> + } > >> + mutex_unlock(&ctrldev->ctrl_lock); > >> + > >> + return ret; > >> }; > >> > >> static const struct file_operations rpmsg_ctrldev_fops = { > >> @@ -119,6 +147,7 @@ static int rpmsg_ctrldev_probe(struct rpmsg_device *rpdev) > >> device_initialize(dev); > >> dev->parent = &rpdev->dev; > >> > >> + mutex_init(&ctrldev->ctrl_lock); > >> cdev_init(&ctrldev->cdev, &rpmsg_ctrldev_fops); > >> ctrldev->cdev.owner = THIS_MODULE; > >> > >> diff --git a/include/uapi/linux/rpmsg.h b/include/uapi/linux/rpmsg.h > >> index f5ca8740f3fb..1637e68177d9 100644 > >> --- a/include/uapi/linux/rpmsg.h > >> +++ b/include/uapi/linux/rpmsg.h > >> @@ -33,4 +33,14 @@ struct rpmsg_endpoint_info { > >> */ > >> #define RPMSG_DESTROY_EPT_IOCTL _IO(0xb5, 0x2) > >> > >> +/** > >> + * Instantiate a new local rpmsg service device. > >> + */ > >> +#define RPMSG_CREATE_DEV_IOCTL _IOW(0xb5, 0x3, struct rpmsg_endpoint_info) > >> + > >> +/** > >> + * Release a local rpmsg device. > >> + */ > >> +#define RPMSG_RELEASE_DEV_IOCTL _IOW(0xb5, 0x4, struct rpmsg_endpoint_info) > >> + > >> #endif > >> -- > >> 2.17.1 > >>