| Message ID | E1pCiUe-00457v-SQ@rmk-PC.armlinux.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] nvmem: fix registration vs use race | expand |
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 fundamental principles of kernel programming: do not publish data 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) <rmk+kernel@armlinux.org.uk> > --- > 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) <rmk+kernel@armlinux.org.uk> > > --- > > 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. :(
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);
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) <rmk+kernel@armlinux.org.uk> --- v2: add fixes tag drivers/nvmem/core.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-)