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nvmem: core: fix registration vs use race

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[ 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fundamental principles of kernel programming: do not publish data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@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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Russell King (Oracle) 2023-01-27 10:40:11 +00:00 committed by Greg Kroah-Hartman
parent 23676ecd2e
commit 2dcb474af1
1 changed files with 7 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/nvmem/core.c
View File

@ -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 @@ err_remove_cells:
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);