nvmem: core: fix registration vs use race

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fundamental principles of kernel programming: do not publish data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")
Cc: stable@vger.kernel.org
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230127104015.23839-7-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index ac77a01..e92c6f1 100644 (file)
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -832,22 +832,16 @@ 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_add(&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) {
@@ -864,6 +858,12 @@ 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_add(&nvmem->dev);
+       if (rval)
+               goto err_remove_cells;
+
        blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
 
        return nvmem;
@@ -873,8 +873,6 @@ err_remove_cells:
 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);