Re: [PATCH v2] nvmem: core: Fix race in nvmem_register()

Srinivas Kandagatla
2023-01-03T12:41:14Z

On 03/01/2023 11:44, Hector Martin wrote:
> nvmem_register() currently registers the device before adding the nvmem
> cells, which creates a race window where consumers may find the nvmem
> device (and not get PROBE_DEFERred), but then fail to find the cells and
> error out.
>
> Move device registration to the end of nvmem_register(), to close the
> race.
>
> Observed when the stars line up on Apple Silicon machines with the (not
> yet upstream, but trivial) spmi nvmem driver and the macsmc-rtc client:
>
> [ 0.487375] macsmc-rtc macsmc-rtc: error -ENOENT: Failed to get rtc_offset NVMEM cell
>
> Fixes: eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
> Cc: stable@vger.kernel.org
> Reviewed-by: Eric Curtin <ecurtin@redhat.com>
> Signed-off-by: Hector Martin <marcan@marcan.st>
> ---

What has changed since v1?

> drivers/nvmem/core.c | 32 +++++++++++++++++---------------
> 1 file changed, 17 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 321d7d63e068..606f428d6292 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -822,11 +822,8 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> break;
> }
>
> - if (rval) {
> - ida_free(&nvmem_ida, nvmem->id);
> - kfree(nvmem);
> - return ERR_PTR(rval);
> - }
> + if (rval)
> + goto err_gpiod_put;

Why was gpiod changes added to this patch, that should be a separate
patch/discussion, as this is not relevant to the issue that you are
reporting.

>
> nvmem->read_only = device_property_present(config->dev, "read-only") ||
> config->read_only || !nvmem->reg_write;
> @@ -837,20 +834,16 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>
> 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_gpiod_put;
> }
>
> if (config->compat) {
> rval = nvmem_sysfs_setup_compat(nvmem, config);
> if (rval)
> - goto err_device_del;
> + goto err_gpiod_put;
> }
>
> if (config->cells) {
> @@ -867,6 +860,15 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> if (rval)
> goto err_remove_cells;
>
> + rval = device_register(&nvmem->dev);
> + if (rval) {
> + nvmem_device_remove_all_cells(nvmem);
> + if (config->compat)
> + nvmem_sysfs_remove_compat(nvmem, config);
> + put_device(&nvmem->dev);
> + return ERR_PTR(rval);
> + }
> +
> blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
>
> return nvmem;
> @@ -876,10 +878,10 @@ 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);
> +err_gpiod_put:
> + gpiod_put(nvmem->wp_gpio);
> + ida_free(&nvmem_ida, nvmem->id);
> + kfree(nvmem);
>
> return ERR_PTR(rval);
> }
> --
> 2.35.1
>