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Subject[PATCH] nvmem: core: Fix race in nvmem_register()
Date
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")
Signed-off-by: Hector Martin <marcan@marcan.st>
---
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..d255feca5e17 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -837,20 +837,16 @@ 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;
+ return ERR_PTR(rval);
}

if (config->compat) {
rval = nvmem_sysfs_setup_compat(nvmem, config);
if (rval)
- goto err_device_del;
+ return ERR_PTR(rval);
}

if (config->cells) {
@@ -867,19 +863,21 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
if (rval)
goto err_remove_cells;

+ rval = device_register(&nvmem->dev);
+ if (rval)
+ goto err_put_device;
+
blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);

return nvmem;

+err_put_device:
+ put_device(&nvmem->dev);
err_remove_cells:
nvmem_device_remove_all_cells(nvmem);
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);

return ERR_PTR(rval);
}
--
2.35.1
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