RE: [PATCH 1/4] fs, afs: convert afs_cell.usage from atomic_t to refcount_t
From: Reshetova, Elena
Date: Wed Feb 22 2017 - 12:20:37 EST
> Elena Reshetova <elena.reshetova@xxxxxxxxx> wrote:
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> This causes an assertion failure because cells aren't immediately destroyed
> when their refcount reaches 0, but may be resurrected provided the cache lock
> is held. However, attempting to increment the 0 refcount does nothing, not
> even giving a warning.
This is strange, it is supposed to give a warning I think now when it is even not inlined.
Peter, am I confusing smth?
> So please place a hold on this patch. I will check the other AFS patches also.
Thank you very much David for testing the patches!
I guess for this one and other two patches it means that if we want to do the atomic_t --> refcount_t conversions,
we need to do +1 on the whole counting scheme to avoid issues around reaching zero.
Do you see this approach reasonable? I can give it a try, if it makes sense in your opinion.