Re: sparse multiple address spaces?

[Randy Dunlap <rdunlap@infradead.org>]

On 8/19/20 1:52 PM, Luc Van Oostenryck wrote:
> On Wed, Aug 19, 2020 at 10:06:55PM +0200, Luc Van Oostenryck wrote:
>> On Wed, Aug 19, 2020 at 12:15:46PM -0700, Randy Dunlap wrote:
>>> On Linux kernel tree v5.9-rc1, with sparse v0.6.2-180-g49f7e13a,
>>> I see this sparse warning which I don't grok:
>>>
>>> ../include/uapi/asm-generic/signal-defs.h:19:29: CK: error: multiple address spaces given
>>>
>>> for this source code:
>>>
>>> typedef void __signalfn_t(int);
>>> typedef __signalfn_t __user *__sighandler_t; <<<<< line 19
>>>
>>> Are there multiple address spaces there?  What are they?
>>>
>>>
>>>
>>> or: is the warning related to the other nearby warnings?  (e.g.:)
>>>
>>> ../kernel/signal.c:541:53: CK: warning: incorrect type in initializer (different address spaces)
>>> ../kernel/signal.c:541:53: CK:    expected struct k_sigaction *ka
>>> ../kernel/signal.c:541:53: CK:    got struct k_sigaction [noderef] __rcu *
>>> ../include/uapi/asm-generic/signal-defs.h:19:29: CK: error: multiple address spaces given
>>> ../kernel/signal.c:694:33: CK: warning: incorrect type in argument 1 (different address spaces)
>>> ../kernel/signal.c:694:33: CK:    expected struct spinlock [usertype] *lock
>>> ../kernel/signal.c:694:33: CK:    got struct spinlock [noderef] __rcu *
>>
>> I would guess that this __sighandler_t is used somewhere in a
>> struct which is itself accessed via a __rcu pointer.
>> But that would not explain the level of dereference.
>>
>> I'll need to check this one.
> 
> The location of the warning should be the assignment in kernel/signal.c:69
> 
> 	static void __user *sig_handler(struct task_struct *t, int sig) 
> 	{
> 		return t->sighand->action[sig - 1].sa.sa_handler;
> 	}
>  
> There is a lot of type abuses in this file, between 'void __user *' and
> __sighandler_t, but the root cause of the warning is the '__rcu' in 
> 
> 	struct task_struct {
> 		...
> 		struct sighand_struct __rcu *sighand;
> 		...
> 	}

OK, thanks for all of your excavation work. :)

-- 
~Randy