Re: [PATCH v4 3/5] liveupdate: block session mutations during reboot

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On 05-18 11:40, Mike Rapoport wrote:
> On Sun, May 17, 2026 at 07:26:48PM +0000, 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@gerlicz.space>
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > ---
> >  kernel/liveupdate/luo_session.c | 27 ++++++++++++++++++++++++---
> >  1 file changed, 24 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
> > index 59b37d17db6b..6099213275d8 100644
> > --- a/kernel/liveupdate/luo_session.c
> > +++ b/kernel/liveupdate/luo_session.c
> > @@ -385,9 +394,12 @@ int luo_session_create(const char *name, struct file **filep)
> >  	struct luo_session *session;
> >  	int err;
> >  
> > +	down_read(&luo_session_serialize_rwsem);
> >  	session = luo_session_alloc(name);
> 
> We can alloc outside the lock, will make error handling simpler.
> 
> sashiko complains about mixing down_read() with scoped_guard(), for this
> function it would make sense to use plain mutex_{lock,unlock} around
> luo_session_getfile()

Done. Thank  you for review.

Pasha

> 
> > -	if (IS_ERR(session))
> > -		return PTR_ERR(session);
> > +	if (IS_ERR(session)) {
> > +		err = PTR_ERR(session);
> > +		goto err_unlock;
> > +	}
> >  
> >  	err = luo_session_insert(&luo_session_global.outgoing, session);
> >  	if (err)
> > @@ -398,12 +410,16 @@ int luo_session_create(const char *name, struct file **filep)
> >  	if (err)
> >  		goto err_remove;
> >  
> > +	up_read(&luo_session_serialize_rwsem);
> > +
> >  	return 0;
> >  
> >  err_remove:
> >  	luo_session_remove(&luo_session_global.outgoing, session);
> >  err_free:
> >  	luo_session_free(session);
> > +err_unlock:
> > +	up_read(&luo_session_serialize_rwsem);
> >  
> >  	return err;
> >  }
> 
> -- 
> Sincerely yours,
> Mike.