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Date: Sat, 16 Jan 2016 22:26:43 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Chagin Dmitry <dchagin@freebsd.org>
Cc: freebsd-hackers@freebsd.org
Subject: Re: irrelevant locking
Message-ID: <20160116202643.GL3942@kib.kiev.ua>
References: <20160116195819.GA41610@chd.heemeyer.club>
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On Sat, Jan 16, 2016 at 10:58:19PM +0300, Chagin Dmitry wrote:
> hi, please, can someone explain the reason to take the process lock here:
There is no reason, I think that the PROC_LOCK() can be removed.

> 
> int
> sys_issetugid(register struct thread *td, struct issetugid_args *uap)
> {
> 	struct proc *p = td->td_proc;
> 
> 	/*
> 	 * Note: OpenBSD sets a P_SUGIDEXEC flag set at execve() time,
> 	 * we use P_SUGID because we consider changing the owners as
> 	 * "tainting" as well.
> 	 * This is significant for procs that start as root and "become"
> 	 * a user without an exec - programs cannot know *everything*
> 	 * that libc *might* have put in their data segment.
> 	 */
> 	PROC_LOCK(p);
> 	td->td_retval[0] = (p->p_flag & P_SUGID) ? 1 : 0;
> 	PROC_UNLOCK(p);
> 	return (0);
> }