Re: [PATCH v3] ipc: introduce ipc_valid_object() helper to sort out IPC_RMID races

[Rafael Aquini <aquini@redhat.com>]

On Wed, Dec 18, 2013 at 04:38:24PM -0800, Davidlohr Bueso wrote:
> On Wed, 2013-12-18 at 18:33 -0200, Rafael Aquini wrote:
> > After the locking semantics for the SysV IPC API got improved, a couple of
> > IPC_RMID race windows were opened because we ended up dropping the
> > 'kern_ipc_perm.deleted' check performed way down in ipc_lock().
> > The spotted races got sorted out by re-introducing the old test within
> > the racy critical sections.
> > 
> > This patch introduces ipc_valid_object() to consolidate the way we cope with
> > IPC_RMID races by using the same abstraction across the API implementation.
> > 
> > Signed-off-by: Rafael Aquini <aquini@redhat.com>
> > Acked-by: Rik van Riel <riel@redhat.com>
> > Acked-by: Greg Thelen <gthelen@google.com>
> 
> Reviewed-by: Davidlohr Bueso <davidlohr@hp.com>
> 
> [...]
> 
> > +/*
> > + * ipc_valid_object() - helper to sort out IPC_RMID races for codepaths
> > + * where the respective ipc_ids.rwsem is not being held down.
> > + * Checks whether the ipc object is still around or if it's gone already, as
> > + * ipc_rmid() may have already freed the ID while the ipc lock was spinning.
> > + * Needs to be called with kern_ipc_perm.lock held -- exception made for one
> > + * checkpoint case at sys_semtimedop() as noted in code commentary.
> > + */
> > +static inline bool ipc_valid_object(struct kern_ipc_perm *perm)
> > +{
> > +	return perm->deleted == 0;
> > +}
> 
> I would like to see .deleted being converted to bool while we're at it
> though, that return statement just bugs the hell out of me. Could you
> send a patch for that as well?
>

Sure, as I mentioned earlier the full .deleted conversion from int to bool
it's on my todo list already for a follow-up patch.

Thanks!
-- Rafael