linux-kernel - Re: [PATCH] kernel/module.c: Free lock-classes if parse

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Date:	Thu, 22 Jan 2015 11:10:30 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrey Tsyvarev <tsyvarev@...ras.ru>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kernel/module.c: Free lock-classes if parse_args failed

Andrey Tsyvarev <tsyvarev@...ras.ru> writes:
> 21.01.2015 4:40, Rusty Russell пишет:
>> Andrey Tsyvarev <tsyvarev@...ras.ru> writes:
>>> 20.01.2015 9:37, Rusty Russell пишет:
>>>> Andrey Tsyvarev <tsyvarev@...ras.ru> writes:
>>>>> parse_args call module parameters' .set handlers, which may use locks defined in the module.
>>>>> So, these classes should be freed in case parse_args returns error(e.g. due to incorrect parameter passed).
>>>> Thanks, this seems right.  Applied.
>>>>
>>>> But this makes me ask: where is lockdep_free_key_range() called on the
>>>> module init code?  It doesn't seem to be at all...
>>> As I understand, locks are not allowed to be defined in the module init
>>> section. So, no needs to call lockdep_free_key_range() for it.
>>> This has a sense: objects from that section are allowed to be used only
>>> by module->init() function. But a single function call doesn't require
>>> any synchronization wrt itself.
>> I don't know that we have any __initdata locks; it would be really
>> weird.
>>
>> But change 'static DEFINE_MUTEX(mutex_param);' to 'static __initdata
>> DEFINE_MUTEX(mutex_param);' to test.
> Compiler warns about sections mismatch, but the test works.
>
> According to lockdep_free_key_range() code, lock class is cleared not 
> only according to
> its key(which is equal to lock address in the case of static lock) but 
> also according to its name.

What happens if you later register another lock at that address, since
the memory is freed?

A quick grep revealed no __initdata locks in the kernel, so I don't
think we care anyway.

Cheers,
Rusty.
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