svn commit: r345100 - head/sys/compat/linuxkpi/common/include/linux

[Konstantin Belousov]

On Wed, Mar 13, 2019 at 06:55:42PM +0000, Hans Petter Selasky wrote:
> Author: hselasky
> Date: Wed Mar 13 18:55:41 2019
> New Revision: 345100
> URL: https://svnweb.freebsd.org/changeset/base/345100
> 
> Log:
>   Implement task_euid() and get_task_state() function macros in the LinuxKPI.
>   
>   Submitted by:		Johannes Lundberg <johalun0 at gmail.com>
>   MFC after:		1 week
>   Sponsored by:		Limelight Networks
>   Sponsored by:		Mellanox Technologies
> 
> Modified:
>   head/sys/compat/linuxkpi/common/include/linux/sched.h
> 
> Modified: head/sys/compat/linuxkpi/common/include/linux/sched.h
> ==============================================================================
> --- head/sys/compat/linuxkpi/common/include/linux/sched.h	Wed Mar 13 18:53:29 2019	(r345099)
> +++ head/sys/compat/linuxkpi/common/include/linux/sched.h	Wed Mar 13 18:55:41 2019	(r345100)
> @@ -95,7 +95,9 @@ struct task_struct {
>  #define	get_pid(x)		(x)
>  #define	put_pid(x)		do { } while (0)
>  #define	current_euid()	(curthread->td_ucred->cr_uid)
> +#define	task_euid(task)	((task)->task_thread->td_ucred->cr_uid)
This looks very strange if you compare the definition of task_euid()
with the definition of linux_task_exiting() in r345098.

There you access td_ucred which is basically volatile and invalid unless
the thread is known to be inhibited or sleeping (and not exiting).  So
to use the macro safely for task not associated with current thread,
you must have very strong and unusual external guarantees.

On the other hand, linux_task_exiting() correctly locks the target process.
But, since the lock is dropped before the function returns, the process
might exit wheh the callers gets to use the result.  Again, some external
guarantees must be ensured to give safe use for this macro as well, for
the target process != curproc.

>  
> +#define	get_task_state(task)		atomic_read(&(task)->state)
>  #define	set_task_state(task, x)		atomic_set(&(task)->state, (x))
>  #define	__set_task_state(task, x)	((task)->state.counter = (x))
>  #define	set_current_state(x)		set_task_state(current, x)