linux-kernel - Re: fs/exec.c:1307:26: sparse: sparse: incorrect type in argument 1 (different address spaces)

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Date: Fri, 12 Jan 2024 16:32:14 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: kernel test robot <lkp@...el.com>, Thadeu Lima de Souza Cascardo
 <cascardo@...onical.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org, "Paul E.
 McKenney" <paulmck@...nel.org>, Christian Brauner <brauner@...nel.org>
Subject: Re: fs/exec.c:1307:26: sparse: sparse: incorrect type in argument 1
 (different address spaces)

On Thu, Jan 11 2024 at 10:44, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   acc657692aed438e9931438f8c923b2b107aebf9
> commit: e362359ace6f87c201531872486ff295df306d13 posix-cpu-timers: Cleanup CPU timers before freeing them during exec
> date:   1 year, 5 months ago

I'm amused that it took 17 month ....

>>> fs/exec.c:1307:26: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct spinlock [usertype] *lock @@     got struct spinlock [noderef] __rcu * @@
>   1305	
>   1306	#ifdef CONFIG_POSIX_TIMERS
>> 1307		spin_lock_irq(&me->sighand->siglock);
>   1308		posix_cpu_timers_exit(me);
>   1309		spin_unlock_irq(&me->sighand->siglock);
>   1310		exit_itimers(me);
>   1311		flush_itimer_signals();
>   1312	#endif

So this warning is clearly wrong because 'current->sighand->siglock' is
safe to dereference w/o RCU protection for 'current'.

The real issue is this commit:

   913292c97d75 ("sched.h: Annotate sighand_struct with __rcu")

which blindly 'fixed' a sparse warning in signal.c w/o even trying to
look at the consequences. There are 170+ instances of spin_[un]lock()
variants which should emit exactly the same warning...

I think the right fix is to annotate this legit case of derefencing
current->sighand->siglock so sparse knows that this is safe.

Thanks,

        tglx