Re: [PATCH 39/41] kernel/fork: throttle call_rcu() calls in vm_area_free

[Michal Hocko]

On Fri 20-01-23 09:50:01, Suren Baghdasaryan wrote:
> On Fri, Jan 20, 2023 at 9:32 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
[...]
> > The page fault handler (or whatever other reader -- ptrace, proc, etc)
> > should have a refcount on the mm_struct, so we can't be in this path
> > trying to free VMAs.  Right?
> 
> Hmm. That sounds right. I checked process_mrelease() as well, which
> operated on mm with only mmgrab()+mmap_read_lock() but it only unmaps
> VMAs without freeing them, so we are still good. Michal, do you agree
> this is ok?

Don't we need RCU procetions for the vma life time assurance? Jann has
already shown how rwsem is not safe wrt to unlock and free without RCU.

-- 
Michal Hocko
SUSE Labs