Date: Fri, 14 Jun 2013 16:56:57 -0400 From: John Baldwin <jhb@freebsd.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: freebsd-current@freebsd.org, Alfred Perlstein <bright@mu.org> Subject: Re: copyin()/copyout() constraints ? Message-ID: <201306141656.57827.jhb@freebsd.org> In-Reply-To: <20130614163812.GA50980@onelab2.iet.unipi.it> References: <20130612180115.GA27892@onelab2.iet.unipi.it> <201306141207.29779.jhb@freebsd.org> <20130614163812.GA50980@onelab2.iet.unipi.it>
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On Friday, June 14, 2013 12:38:12 pm Luigi Rizzo wrote: > On Fri, Jun 14, 2013 at 12:07:29PM -0400, John Baldwin wrote: > > On Wednesday, June 12, 2013 2:36:52 pm Alfred Perlstein wrote: > > > On 6/12/13 11:01 AM, Luigi Rizzo wrote: > > > > hi, > > > > is it possible to run copyin() or copyout() in one of these cases: > > > > 1. while holding a spinlock > > > > 2. while holding a regular mutex/lock > > > > 3. while holding a read lock (on an RWLOCK or RMLOCK) > > > > 4. while holding a write lock (on an RWLOCK or RMLOCK) > > > > > > > > I suspect #1 is forbidden, but am a bit unclear for the > > > > other cases. > > > No on all of the above unless the memory is wired. > > ok i suppose i'll move to an sx lock, which i have been told > allows me to sleep ? > > My use case is that while i run the copyin(), and possibly take a > page fault, nobody destroys the destination buffer. So i wanted > to hold a read lock (sx_slock() ?) in the thread doing the copy > (there may be several writers to different parts of the destination), > and a write lock (sx_xlock() ?) for the other thread which may > destroy the buffer. Yep, that will work fine. -- John Baldwin
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