[PATCH v6 3/5] liveupdate: block session mutations during reboot

[Mike Rapoport]

On Thu, May 28, 2026 at 04:20:53PM +0200, Pratyush Yadav wrote:
> On Wed, May 27 2026, Pasha Tatashin wrote:
> 
> > During the reboot() syscall, user processes may still be running
> > concurrently and attempting to mutate sessions (e.g., creating,
> > retrieving, or releasing sessions). To prevent this, introduce
> > luo_session_serialize_rwsem to synchronize mutations with the
> > serialization process.
> >
> > All session mutation operations (create, retrieve, release, ioctl) take
> > the read lock. The serialization process (luo_session_serialize) takes
> > the write lock and holds it indefinitely on success. This effectively
> > freezes the LUO session subsystem during the transition to the new
> > kernel. If serialization fails, the lock is released to allow recovery.
> >
> > Fixes: 0153094d03df ("liveupdate: luo_session: add sessions support")
> > Reported-by: Oskar Gerlicz Kowalczuk <oskar at gerlicz.space>
> > Acked-by: Mike Rapoport (Microsoft) <rppt at kernel.org>
> > Signed-off-by: Pasha Tatashin <pasha.tatashin at soleen.com>
> > ---
> >  kernel/liveupdate/luo_session.c | 56 +++++++++++++++++++++++++++++++--
> >  1 file changed, 53 insertions(+), 3 deletions(-)
> >  
> > +/*
> > + * Protects session mutations during serialization. All session mutation
> > + * operations must hold the read lock. The serialization process holds the write
> > + * lock indefinitely on success to block all concurrent and future mutations.
> > + */
> 
> Nit: this comment is redundant now. I guess you can remove this when
> applying.

Done :)
 
> Reviewed-by: Pratyush Yadav (Google) <pratyush at kernel.org>
> 
> > +static DECLARE_RWSEM(luo_session_serialize_rwsem);
> > +
> >  /**
> >   * struct luo_session_header - Header struct for managing LUO sessions.
> >   * @count:      The number of sessions currently tracked in the @list.
> [...]
> 
> -- 
> Regards,
> Pratyush Yadav

-- 
Sincerely yours,
Mike.