Re: copyin()/copyout() constraints ?

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