Re: [PATCH] Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()"

[Manfred Spraul]

Hello together,

On 12/17/19 10:17 PM, Herton R. Krzesinski wrote:
> On Mon, Dec 16, 2019 at 08:04:53PM +0100, Manfred Spraul wrote:
> > Hi Ioanna,
> >
> > On 12/11/19 8:13 PM, Ioanna Alifieraki wrote:
> >
> > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1694779
> > >
> > > Fixes: a97955844807 ("ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()")
> > > Signed-off-by: Ioanna Alifieraki <ioanna-maria.alifieraki@xxxxxxxxxxxxx>
> > Acked-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
> Acked-by: Herton R. Krzesinski <herton@xxxxxxxxxx>

What I forgot:

I think Cc: stable@xxxxxxxxxxxxxxx should be added:

The change is obviously correct, it fixes a real issue.

> > > ---
> > >    ipc/sem.c | 6 ++----
> > >    1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/ipc/sem.c b/ipc/sem.c
> > > index ec97a7072413..fe12ea8dd2b3 100644
> > > --- a/ipc/sem.c
> > > +++ b/ipc/sem.c
> > > @@ -2368,11 +2368,9 @@ void exit_sem(struct task_struct *tsk)
> > >    		ipc_assert_locked_object(&sma->sem_perm);
> > >    		list_del(&un->list_id);
> > > -		/* we are the last process using this ulp, acquiring ulp->lock
> > > -		 * isn't required. Besides that, we are also protected against
> > > -		 * IPC_RMID as we hold sma->sem_perm lock now
> > > -		 */
> > > +		spin_lock(&ulp->lock);
> > >    		list_del_rcu(&un->list_proc);
> > > +		spin_unlock(&ulp->lock);
> > >    		/* perform adjustments registered in un */
> > >    		for (i = 0; i < sma->sem_nsems; i++) {