svn commit: r232181 - in head/sys: kern sys

[Konstantin Belousov]

On Wed, Feb 29, 2012 at 09:36:02AM -0500, John Baldwin wrote:
> On Wednesday, February 29, 2012 8:25:07 am Konstantin Belousov wrote:
> > On Wed, Feb 29, 2012 at 02:37:25PM +0200, Mikolaj Golub wrote:
> > > 
> > > On Wed, 29 Feb 2012 12:03:00 +0000 Robert N. M. Watson wrote:
> > > 
> > >  RNMW> I think the monitoring aspect of the patch is fine.
> > > 
> > >  RNMW> The bit I was worried about was external umask changes. This can cause
> > >  RNMW> race conditions for applications that manage their umask -- for
> > >  RNMW> example, bsdtar, if I recall correctly. It's one thing to use a
> > >  RNMW> debugger to force an application to change its umask -- the developer
> > >  RNMW> needs to know they are changing application behaviour. But exposing a
> > >  RNMW> feature that can lead to correct applications but incorrect results is
> > >  RNMW> a risky thing to do, hence my objection.
> > > 
> > >  RNMW> I think given the other objections, it would be wise to remove write
> > >  RNMW> access to process umasks, but retain read access for procstat (which is
> > >  RNMW> quite useful, I agree).
> > > 
> > > I still don't see why having a sysctl RW is worse than asking users to run
> > > something like in the attach when they need to change umask for another
> > > process, but ok, if people don't like RW I will remove it.
> > > 
> > What is done is attach is much worse then the sysctl, just because
> > debugger attach often causes spurious EINTR, indeed seriously disrupting
> > applications, as opposed to some uncertain damage that could be done in
> > theory.
> 
> kgdb doesn't though, and presumably for umask you would change it via kgdb, so
> from the running process' perspective it would look the same as changing it via
> sysctl.

Right, but an idea of the change was to allow to do this for somebody who
does not know how to perform it in kgdb. Not to mention that kgdb -w
is risky, e.g. because filedesc might have changed under kgdb, so you would
write over freed memory.
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