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Date: Mon, 26 Dec 2016 13:04:01 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: jinjun gao <gjinjun@gmail.com>
Cc: freebsd-threads@freebsd.org
Subject: Re: Why need not to PROC_UNLOCK() in
 kthread_suspend()/kproc_suspend()?
Message-ID: <20161226110400.GP94325@kib.kiev.ua>
References: <CAORc1LBjzrADNr5_-zg1nt5qDRPVRyzUpRQxkuWCOMtb2QG9dQ@mail.gmail.com>
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On Mon, Dec 26, 2016 at 06:26:48PM +0800, jinjun gao wrote:
> Hi Guys,
> 
> In file sys/kern/kern_kthread.c (
> https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_kthread.c),
> the PROC_LOCK() and PROC_UNLOCK() are used in pairs in one function except
> function kthread_suspend()/kproc_suspend() (
> https://github.com/freebsd/freebsd/blob/master/sys/kern/kern_kthread.c#L177).
> In these two functions, there is only PROC_LOCK(). I checked may related
> function(such as kproc_resume()) and can not find PROC_UNLOCK() to pair the
> one resided in kproc_suspend().  Why need not PROC_UNLOCK() to pair
> PROC_LOCK() in kproc_suspend()/kthread_suspend()? Thanks!
> 
Because later msleep(9) is called with the process lock and PDROP flag.