Patch "nvmem: core: fix registration vs use race" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nvmem: core: fix registration vs use race

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nvmem-core-fix-registration-vs-use-race.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f35e9aab2eb8882b2e4536ba56a9a73a972fd6a6
Author: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Date:   Fri Jan 27 10:40:11 2023 +0000

    nvmem: core: fix registration vs use race
    
    [ Upstream commit ab3428cfd9aa2f3463ee4b2909b5bb2193bd0c4a ]
    
    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    fundamental principles of kernel programming: do not publish data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@xxxxxxxxxxxxxxx
    Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
    Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230127104015.23839-7-srinivas.kandagatla@xxxxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index de356cdde4ce8..0ef7b95348b1b 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -682,16 +682,10 @@ 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 (config->compat) {
 		rval = nvmem_sysfs_setup_compat(nvmem, config);
 		if (rval)
-			goto err_device_del;
+			goto err_put_device;
 	}
 
 	if (config->cells) {
@@ -708,6 +702,12 @@ 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;
@@ -716,8 +716,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	nvmem_device_remove_all_cells(nvmem);
 	if (config->compat)
 		nvmem_sysfs_remove_compat(nvmem, config);
-err_device_del:
-	device_del(&nvmem->dev);
 err_put_device:
 	put_device(&nvmem->dev);