On Thu, Sep 11, 2014 at 11:52:02PM +0200, Thomas Gleixner wrote: > On Thu, 11 Sep 2014, Dave Jones wrote: > > > Hit this overnight on Linus tree from yesterday. > > > > BUG: sleeping function called from invalid context at > > include/linux/freezer.h:56 > > in_atomic(): 1, irqs_disabled(): 0, pid: 31948, name: trinity-c121 > > Preemption disabled at:[<ffffffffb90f2512>] futex_wait_setup+0xb2/0x140 > > Huch? So we are in a preempt disabled region in futex_wait_setup and > we get interrupted and end up in the signal delivery path? > > I really love that futex stuff.... > > But fortunately the preemption disabled hint made it into mainline so > looking at the callsites of futex_wait_setup() makes it pretty clear > where the shit hits the fan. Patch below. > > Thanks, > > tglx > > -------------------> > From: Thomas Gleixner <[email protected]> > Date: Thu, 11 Sep 2014 23:44:35 +0200 > Subject: futex: Unlock hb->lock in futex_wait_requeue_pi() error path > > futex_wait_requeue_pi() calls futex_wait_setup(). If > futex_wait_setup() succeeds it returns with hb->lock held and > preemption disabled. Now the sanity check after this does: > > if (match_futex(&q.key, &key2)) { > ret = -EINVAL; > goto out_put_keys; > } > > which releases the keys but does not release hb->lock. So we happily > return to user space with hb->lock held and therefor preemption > disabled. > > Unlock hb->lock before taking the exit route. > > Reported-by: Dave "Trinity" Jones <[email protected]> > Signed-off-by: Thomas Gleixner <[email protected]> > --- > diff --git a/kernel/futex.c b/kernel/futex.c > index d3a9d946d0b7..815d7af2ffe8 100644 > --- a/kernel/futex.c > +++ b/kernel/futex.c > @@ -2592,6 +2592,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, > unsigned int flags, > * shared futexes. We need to compare the keys: > */ > if (match_futex(&q.key, &key2)) { > + queue_unlock(hb); > ret = -EINVAL; > goto out_put_keys; > }
I was hoping to move this before the key equivalence test so we could exit as early as possible, but some idgit (that would be me) embedded the get_futex_key() for uaddr into futex_wait_setup() to avoid so much duplication of code... sigh. Thomas's fix is the best immediate solution in my opinion. Reviewed-by: Darren Hart <[email protected]> -- Darren Hart Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
