Re: [PATCH v2 1/2] mm: Add an F_SEAL_FS_WRITE seal to memfd

[Christoph Hellwig]

On Wed, Oct 17, 2018 at 08:44:01AM -0700, Daniel Colascione wrote:
> > Even if no one changes these specific flags we still need a lock due
> > to rmw cycles on the field.  For example fadvise can set or clear
> > FMODE_RANDOM.  It seems to use file->f_lock for synchronization.
> 
> Compare-and-exchange will suffice, right?

Only if all users use the compare and exchange, and right now they
don't.