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Message-ID: <bad6a162-3e82-2f5e-1822-23951b61450b@linaro.org>
Date: Tue, 3 Jan 2023 11:30:36 +0000
From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Hector Martin <marcan@...can.st>
Subject: Re: [PATCH] nvmem: fix registration vs use race
On 03/01/2023 09:42, 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 fundamental principles of kernel programming: do not publish data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.
>
how about a Fixes tag and Cc stable?
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> ---
> 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;
AFAIU, as we never did a get_device/kobject_get, calling put_device at
this point will not invoke a release callback which can potentially leak
both nvmem and ida.
--srini
> }
>
> 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);
>
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