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From: John Baldwin <jhb@freebsd.org>
To: Julian Elischer <julian@elischer.org>
Date: Thu, 24 Aug 2006 16:47:55 -0400
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Cc: cvs-src@freebsd.org, src-committers@freebsd.org,
	Konstantin Belousov <kib@freebsd.org>, cvs-all@freebsd.org
Subject: Re: cvs commit: src/share/man/man9 lock.9
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On Thursday 24 August 2006 16:16, Julian Elischer wrote:
> Konstantin Belousov wrote:
> 
> >kib         2006-08-24 10:16:01 UTC
> >
> >  FreeBSD src repository
> >
> >  Modified files:        (Branch: RELENG_6)
> >    share/man/man9       lock.9 
> >  Log:
> >  MFC rev.1.14:
> >  Note that LK_UPGRADE may drop the shared lock before taking the
> >  exclusive one.
> >  
> >  
> >
> excuse my ignorance but I though that the whole aim of an upgrade was to 
> make sure that
> you did NOT drop it before getting the exclusive lock..( or it fails and 
> you back out and retry)

This is why sx and rw locks only have a try_upgrade and not a blocking
upgrade.  The calling code can then do a sunlock and blocking xlock
and make sure they redo any needed checks, etc.

> >  Reviewed and edited by: tegge
> >  Approved by:    pjd (mentor)
> >  
> >  Revision  Changes    Path
> >  1.12.2.2  +2 -0      src/share/man/man9/lock.9
> >  
> >
> 

-- 
John Baldwin