Messages in this thread | | | Date | Tue, 21 Dec 2021 18:46:01 +0100 | Subject | Re: [PATCH] nvmem: fix unregistering device in nvmem_register() error path | From | Rafał Miłecki <> |
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On 21.12.2021 17:06, Greg Kroah-Hartman wrote: > On Tue, Dec 21, 2021 at 04:45:50PM +0100, Rafał Miłecki wrote: >> From: Rafał Miłecki <rafal@milecki.pl> >> >> 1. Drop incorrect put_device() calls >> >> If device_register() fails then underlaying device_add() takes care of >> calling put_device() if needed. There is no need to do that in a driver. > > Did you read the documentation for device_register() that says: > > * NOTE: _Never_ directly free @dev after calling this function, even > * if it returned an error! Always use put_device() to give up the > * reference initialized in this function instead.
I clearly tried to be too smart and ignored documentation.
I'd say device_add() behaviour is rather uncommon and a bit unintuitive. Most kernel functions are safe to assume to do nothing that requires cleanup if they fail.
E.g. if I call platform_device_register() and it fails I don't need to call anything like platform_device_put(). I just free previously allocated memory.
When calling device_register() / device_add() it seems device always gets partially registered (even if it fails!). Enough to make it safe to depend on core subsystem calling .release() after device_put().
So what initially looks like unbalanced device_put() call is actually some device_add() specific magic behaviour ;)
Sorry. I should have checked documentation before posting patches. That's not my best day.
>> 2. Use device_unregister() >> >> Now that we don't call put_device() we can use above helper. >> >> Fixes: 3360acdf8391 ("nvmem: core: fix leaks on registration errors") >> Cc: Johan Hovold <johan@kernel.org> >> Signed-off-by: Rafał Miłecki <rafal@milecki.pl> >> --- >> That put_device() was explicitly added by Johan but after checking >> device_register() twice I still think it's incorrect. I hope I didn't >> miss sth obvious and I didn't mess it up. >> --- >> drivers/nvmem/core.c | 10 ++++------ >> 1 file changed, 4 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c >> index 785a56e33f69..f7f31af7226f 100644 >> --- a/drivers/nvmem/core.c >> +++ b/drivers/nvmem/core.c >> @@ -901,12 +901,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config) >> >> rval = device_register(&nvmem->dev); >> if (rval) >> - goto err_put_device; >> + return ERR_PTR(rval); > > Where do you call put_device() to free the allocated memory? > > You just leaked the kzalloc() call to allocate the memory pointed to by > nvmem :( > > I think the code is fine as-is.
Yeah, I forgot about:
ida_free(&nvmem_ida, nvmem->id); kfree(nvmem);
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