Re: [PATCH] mm: use in_atomic() in print_vma_addr()

[Michal Hocko <mhocko@kernel.org>]

On Mon 06-11-17 11:05:58, Peter Zijlstra wrote:
> On Sun, Nov 05, 2017 at 09:19:46AM +0100, Michal Hocko wrote:
> > [CC Peter]
> > 
> > On Fri 03-11-17 20:09:49, Bart Van Assche wrote:
> > > On Fri, 2017-11-03 at 11:02 -0700, Andrew Morton wrote:
> > > > Also, checkpatch says
> > > > 
> > > > WARNING: use of in_atomic() is incorrect outside core kernel code
> > > > #43: FILE: mm/memory.c:4491:
> > > > +       if (in_atomic())
> > > > 
> > > > I don't recall why we did that, but perhaps this should be revisited?
> > > 
> > > Is the comment above in_atomic() still up-to-date? From <linux/preempt.h>:
> > > 
> > > /*
> > >  * Are we running in atomic context?  WARNING: this macro cannot
> > >  * always detect atomic context; in particular, it cannot know about
> > >  * held spinlocks in non-preemptible kernels.  Thus it should not be
> > >  * used in the general case to determine whether sleeping is possible.
> > >  * Do not use in_atomic() in driver code.
> > >  */
> > > #define in_atomic()	(preempt_count() != 0)
> > 
> > I can still see preempt_disable NOOP for !CONFIG_PREEMPT_COUNT kernels
> > which makes me think this is still a valid comment.
> 
> Yes the comment is very much accurate.

Which suggests that print_vma_addr might be problematic, right?
Shouldn't we do trylock on mmap_sem instead?

-- 
Michal Hocko
SUSE Labs