The i.MX6 CPU frequency driver sometimes fails to register at boot time
due to nvmem_cell_read_u32() sporadically returning -ENOENT.
This happens because there is a window where __nvmem_device_get() in
of_nvmem_cell_get() is able to return the nvmem device, but as cells
have been setup, nvmem_find_cell_entry_by_node() returns NULL.
The occurs because the nvmem core registration code violates one of the
fundamental principles of kernel programming: do not publish data
structures before their setup is complete.
Fix this by making nvmem core code conform with this principle.
Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
Signed-off-by: Russell King (Oracle) <[email protected]>
---
v2: add fixes tag
drivers/nvmem/core.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 321d7d63e068..6b89fb6fa582 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -835,22 +835,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
nvmem->dev.groups = nvmem_dev_groups;
#endif
- dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
-
- rval = device_register(&nvmem->dev);
- if (rval)
- goto err_put_device;
-
if (nvmem->nkeepout) {
rval = nvmem_validate_keepouts(nvmem);
if (rval)
- goto err_device_del;
+ goto err_put_device;
}
if (config->compat) {
rval = nvmem_sysfs_setup_compat(nvmem, config);
if (rval)
- goto err_device_del;
+ goto err_put_device;
}
if (config->cells) {
@@ -867,6 +861,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
if (rval)
goto err_remove_cells;
+ dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
+
+ rval = device_register(&nvmem->dev);
+ if (rval)
+ goto err_remove_cells;
+
blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
return nvmem;
@@ -876,8 +876,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
err_teardown_compat:
if (config->compat)
nvmem_sysfs_remove_compat(nvmem, config);
-err_device_del:
- device_del(&nvmem->dev);
err_put_device:
put_device(&nvmem->dev);
--
2.30.2
On 03/01/2023 23.42, Russell King (Oracle) wrote:
> The i.MX6 CPU frequency driver sometimes fails to register at boot time
> due to nvmem_cell_read_u32() sporadically returning -ENOENT.
>
> This happens because there is a window where __nvmem_device_get() in
> of_nvmem_cell_get() is able to return the nvmem device, but as cells
> have been setup, nvmem_find_cell_entry_by_node() returns NULL.
>
> The occurs because the nvmem core registration code violates one of the
> fundamental principles of kernel programming: do not publish data
> structures before their setup is complete.
>
> Fix this by making nvmem core code conform with this principle.
>
> Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
> Signed-off-by: Russell King (Oracle) <[email protected]>
> ---
> v2: add fixes tag
>
> drivers/nvmem/core.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 321d7d63e068..6b89fb6fa582 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -835,22 +835,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> nvmem->dev.groups = nvmem_dev_groups;
> #endif
>
> - dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
> -
> - rval = device_register(&nvmem->dev);
> - if (rval)
> - goto err_put_device;
> -
> if (nvmem->nkeepout) {
> rval = nvmem_validate_keepouts(nvmem);
> if (rval)
> - goto err_device_del;
> + goto err_put_device;
You can't call put_device() on a device that hasn't gone through
device_initialize() yet.
> }
>
> if (config->compat) {
> rval = nvmem_sysfs_setup_compat(nvmem, config);
> if (rval)
> - goto err_device_del;
> + goto err_put_device;
Ditto.
> }
>
> if (config->cells) {
> @@ -867,6 +861,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> if (rval)
> goto err_remove_cells;
>
> + dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
> +
> + rval = device_register(&nvmem->dev);
> + if (rval)
> + goto err_remove_cells;
> +
> blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
>
> return nvmem;
> @@ -876,8 +876,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> err_teardown_compat:
> if (config->compat)
> nvmem_sysfs_remove_compat(nvmem, config);
> -err_device_del:
> - device_del(&nvmem->dev);
> err_put_device:
> put_device(&nvmem->dev);
>
- Hector
On Wed, Jan 04, 2023 at 12:20:15AM +0900, Hector Martin wrote:
> On 03/01/2023 23.42, Russell King (Oracle) wrote:
> > The i.MX6 CPU frequency driver sometimes fails to register at boot time
> > due to nvmem_cell_read_u32() sporadically returning -ENOENT.
> >
> > This happens because there is a window where __nvmem_device_get() in
> > of_nvmem_cell_get() is able to return the nvmem device, but as cells
> > have been setup, nvmem_find_cell_entry_by_node() returns NULL.
> >
> > The occurs because the nvmem core registration code violates one of the
> > fundamental principles of kernel programming: do not publish data
> > structures before their setup is complete.
> >
> > Fix this by making nvmem core code conform with this principle.
> >
> > Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
> > Signed-off-by: Russell King (Oracle) <[email protected]>
> > ---
> > v2: add fixes tag
> >
> > drivers/nvmem/core.c | 18 ++++++++----------
> > 1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> > index 321d7d63e068..6b89fb6fa582 100644
> > --- a/drivers/nvmem/core.c
> > +++ b/drivers/nvmem/core.c
> > @@ -835,22 +835,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> > nvmem->dev.groups = nvmem_dev_groups;
> > #endif
> >
> > - dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
> > -
> > - rval = device_register(&nvmem->dev);
> > - if (rval)
> > - goto err_put_device;
> > -
> > if (nvmem->nkeepout) {
> > rval = nvmem_validate_keepouts(nvmem);
> > if (rval)
> > - goto err_device_del;
> > + goto err_put_device;
>
> You can't call put_device() on a device that hasn't gone through
> device_initialize() yet.
Right, which is what I just realised while writing the previous reply.
We need to use device_initialize() and device_add(), so we can call
put_device() on it.
Error paths are difficult to properly test. :(
--
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