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Message-ID: <20241024154414.qm6qfzhr7cqzciel@4VRSMR2-DT.corp.robot.car>
Date: Thu, 24 Oct 2024 08:44:14 -0700
From: Russ Weight <russ.weight@...ux.dev>
To: Dionna Glaze <dionnaglaze@...gle.com>
Cc: linux-kernel@...r.kernel.org, Ashish.Kalra@....com,
Luis Chamberlain <mcgrof@...nel.org>,
Danilo Krummrich <dakr@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 1/1] firmware_loader: Move module refcounts to allow
unloading
On Wed, Oct 23, 2024 at 01:17:07PM -0700, Russ Weight wrote:
>
> On Tue, Oct 15, 2024 at 08:14:24PM +0000, Dionna Glaze wrote:
> > If a kernel module registers a firmware upload API ops set, then it's
> > unable to be moved due to effectively a cyclic reference that the module
> > depends on the upload which depends on the module.
> >
> > Instead, only require the try_module_get when an upload is requested to
> > disallow unloading a module only while the upload is in progress.
>
> Generally, the parent driver that registers for firmware_upload would
> want the module to be present until it unregisters.
>
> Is there a case where this change is needed?
>
> >
> > CC: Luis Chamberlain <mcgrof@...nel.org>
> > CC: Russ Weight <russ.weight@...ux.dev>
> > CC: Danilo Krummrich <dakr@...hat.com>
> > CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > CC: "Rafael J. Wysocki" <rafael@...nel.org>
> >
> > Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
> > ---
> > drivers/base/firmware_loader/sysfs_upload.c | 28 ++++++++++++++-------
> > 1 file changed, 19 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/base/firmware_loader/sysfs_upload.c b/drivers/base/firmware_loader/sysfs_upload.c
> > index 829270067d16..97b0ae855b5f 100644
> > --- a/drivers/base/firmware_loader/sysfs_upload.c
> > +++ b/drivers/base/firmware_loader/sysfs_upload.c
> > @@ -103,6 +103,10 @@ static ssize_t cancel_store(struct device *dev, struct device_attribute *attr,
> > if (fwlp->progress == FW_UPLOAD_PROG_IDLE)
> > ret = -ENODEV;
> >
> > + /*
> > + * Not idle, so fw_upload_start already called try_module_get.
> > + * No need to get/put around cancel.
> > + */
>
> This comment isn't necessary. Cancel is intended to signal the
> parent driver to abort the upload by returning an error condition
> from other ops in progress. It shouldn't attempt to unload the
> module.
>
> > fwlp->ops->cancel(fwlp->fw_upload);
> > mutex_unlock(&fwlp->lock);
> >
> > @@ -164,11 +168,13 @@ static void fw_upload_main(struct work_struct *work)
> > enum fw_upload_err ret;
> > struct device *fw_dev;
> > struct fw_upload *fwl;
> > + struct module *module;
> >
> > fwlp = container_of(work, struct fw_upload_priv, work);
> > fwl = fwlp->fw_upload;
> > fw_sysfs = (struct fw_sysfs *)fwl->priv;
> > fw_dev = &fw_sysfs->dev;
> > + module = fwlp->module;
> >
> > fw_upload_update_progress(fwlp, FW_UPLOAD_PROG_PREPARING);
> > ret = fwlp->ops->prepare(fwl, fwlp->data, fwlp->remaining_size);
> > @@ -204,6 +210,7 @@ static void fw_upload_main(struct work_struct *work)
> > fwlp->ops->cleanup(fwl);
> >
> > putdev_exit:
> > + module_put(module);
>
> Skip the local variable: module_put(fwlp->module)
>
> > put_device(fw_dev->parent);
> >
> > /*
> > @@ -238,7 +245,11 @@ int fw_upload_start(struct fw_sysfs *fw_sysfs)
> > return 0;
> > }
> >
> > +
> > fwlp = fw_sysfs->fw_upload_priv;
> > + if (!try_module_get(fwlp->module)) /* released in fw_upload_main */
>
> Isn't it too late to ensure that the module is present? The
> fw_upload_start() function itself resides within the
> syfs_upload module. If the module isn't present, then this function
> cannot be called. try_module_get() would need to be called before
> the call to fw_upload_start().
You can disregard the above comment. I was thinking of THIS module,
instead of the module associated with the driver using the API.
This placement of try_module_get() should be okay.
- Russ
>
> > + return -EFAULT;
> > +
> > mutex_lock(&fwlp->lock);
> >
> > /* Do not interfere with an on-going fw_upload */
> > @@ -310,13 +321,10 @@ firmware_upload_register(struct module *module, struct device *parent,
> > return ERR_PTR(-EINVAL);
> > }
> >
> > - if (!try_module_get(module))
> > - return ERR_PTR(-EFAULT);
> > -
> > fw_upload = kzalloc(sizeof(*fw_upload), GFP_KERNEL);
> > if (!fw_upload) {
> > ret = -ENOMEM;
> > - goto exit_module_put;
> > + goto exit_err;
> > }
> >
> > fw_upload_priv = kzalloc(sizeof(*fw_upload_priv), GFP_KERNEL);
> > @@ -358,7 +366,7 @@ firmware_upload_register(struct module *module, struct device *parent,
> > if (ret) {
> > dev_err(fw_dev, "%s: device_register failed\n", __func__);
> > put_device(fw_dev);
> > - goto exit_module_put;
> > + goto exit_err;
> > }
> >
> > return fw_upload;
> > @@ -372,8 +380,7 @@ firmware_upload_register(struct module *module, struct device *parent,
> > free_fw_upload:
> > kfree(fw_upload);
> >
> > -exit_module_put:
> > - module_put(module);
> > +exit_err:
> >
> > return ERR_PTR(ret);
> > }
> > @@ -387,7 +394,6 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
> > {
> > struct fw_sysfs *fw_sysfs = fw_upload->priv;
> > struct fw_upload_priv *fw_upload_priv = fw_sysfs->fw_upload_priv;
> > - struct module *module = fw_upload_priv->module;
> >
> > mutex_lock(&fw_upload_priv->lock);
> > if (fw_upload_priv->progress == FW_UPLOAD_PROG_IDLE) {
> > @@ -395,6 +401,11 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
> > goto unregister;
> > }
> >
> > + /*
> > + * No need to try_module_get/module_put around the op since only the
> > + * module itself will call unregister, usually when the refcount has
> > + * dropped to zero and it's cleaning up dependencies to destroy itself.
> > + */
>
> This comment is unnecessary.
>
> Thanks,
> - Russ
>
> > fw_upload_priv->ops->cancel(fw_upload);
> > mutex_unlock(&fw_upload_priv->lock);
> >
> > @@ -403,6 +414,5 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
> >
> > unregister:
> > device_unregister(&fw_sysfs->dev);
> > - module_put(module);
> > }
> > EXPORT_SYMBOL_GPL(firmware_upload_unregister);
> > --
> > 2.47.0.rc1.288.g06298d1525-goog
> >
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