Date: Fri, 14 Jun 2013 14:59:57 -0700 From: Alfred Perlstein <bright@mu.org> To: freebsd-current@freebsd.org Subject: Re: copyin()/copyout() constraints ? Message-ID: <51BB925D.2000609@mu.org> In-Reply-To: <20130614163812.GA50980@onelab2.iet.unipi.it> References: <20130612180115.GA27892@onelab2.iet.unipi.it> <51B8BFC4.303@mu.org> <201306141207.29779.jhb@freebsd.org> <20130614163812.GA50980@onelab2.iet.unipi.it>
next in thread | previous in thread | raw e-mail | index | archive | help
On 6/14/13 9:38 AM, 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. We may be putting cart before horse, or horse into cart or something. :) You may want to just wire the user buffer so it can't get ripped out from under you. See John's email which may be helpful to do that. -- Alfred Perlstein VP Software Engineering, iXsystems
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?51BB925D.2000609>